Water treatment chemicals are 16 families of chemicals and media, from coagulants to filter media, that operators and utilities dose into boiler, cooling, membrane, wastewater and drinking water systems to remove contaminants and to control scale, corrosion and microbes. With 124 individual chemicals and media behind those 16 families, which one does what, at what dose and under which rule?
The 16 families follow one order throughout this page: coagulants, flocculants, scale inhibitors, phosphates, corrosion inhibitors, oxygen scavengers, neutralizing amines, non-oxidizing biocides, oxidants and oxidizing biocides, pH adjustment chemicals, dechlorination chemicals, chelating agents, defoamers and antifoams, descaling and cleaning chemicals, ion exchange resins, and adsorbents and filter media.
Every family carries a dose on a named basis, such as 0.50 mg/L (ppm) of alkalinity as CaCO3 consumed per mg/L of dry alum, or 2 to 5 mg/L of HEDP as active in a cooling tower. The top 10 chemicals are chosen by a checkable rule: each sits on the US EPA list of 36 chemicals used in water treatment (47 supply-chain profiles in total) and has a current AWWA B-standard. Drinking water chemicals carry NSF/ANSI/CAN 60 maximum use levels stated as product, and residual limits such as the maximum residual disinfectant level of 4.0 mg/L as Cl2 cap the dose that reaches the tap.
Every value on this page is checked against primary sources (NSF listings, eCFR, AWWA, CEN, EPA, EUR-Lex, WHO); see our methodology and fact-checking process.
What Are Water Treatment Chemicals?#
Water treatment chemicals are the chemicals and media that an operator, engineer or utility doses or specifies to treat water in an industrial, municipal or utility system. The definition covers liquids and solids fed by pump or feeder, such as alum, sodium hypochlorite and caustic soda, and the solid media that water passes through, such as granular activated carbon, filter sand and ion exchange resin.
The two groups differ in certification. Dosed drinking water chemicals are certified under NSF/ANSI/CAN 60, while filter media, granular and powdered activated carbon, activated alumina, zeolite, diatomaceous earth and ion exchange resins are certified under NSF/ANSI/CAN 61 as process media; calcium carbonate and magnesium oxide are the NSF/ANSI/CAN 60 exceptions. Commodity chemicals such as sulfuric acid or soda ash count only in their water treatment role, and swimming pool, spa, household and emergency uses fall outside this reference.
What do water treatment chemicals do?#
Water treatment chemicals do 5 jobs: they remove contaminants, control scale, control corrosion, control microbes and condition water for a process. The 5 jobs map onto the 16 families as listed below.
- Removal: coagulants, flocculants, adsorbents, filter media and ion exchange resins take out particles, color, organic matter, phosphorus and selected ions.
- Scale control: scale inhibitors, chelating agents and descaling chemicals keep calcium carbonate, calcium sulfate and silica off heat-transfer surfaces and membranes.
- Corrosion control: phosphates, corrosion inhibitors, oxygen scavengers and neutralizing amines protect pipes, boilers and condensate lines.
- Microbial control: oxidants and non-oxidizing biocides disinfect drinking water and control biofilm and Legionella in cooling systems.
- Conditioning: pH adjustment chemicals, dechlorination chemicals and defoamers set pH and alkalinity, remove residual chlorine and collapse foam.
Each job rests on one mechanism, such as charge neutralization for coagulants, threshold inhibition for scale inhibitors and film formation for corrosion inhibitors. Those mechanisms, together with alkalinity, saturation and disinfection kinetics, are explained among the water treatment chemistry concepts that underpin every dose on this page.
Where are chemicals dosed in the water treatment process?#
Chemicals are dosed at 4 kinds of points: at the intake or rapid mix, after filtration, at the contact tank, and immediately ahead of the equipment they protect. A drinking water plant feeds coagulant and pH adjustment chemicals at rapid mix, then disinfectant, corrosion inhibitor and fluoride after filtration. A reverse osmosis (RO) plant doses dechlorination chemical ahead of the membranes, because polyamide membranes tolerate less than 0.1 mg/L of free chlorine (DuPont FilmTec Reverse Osmosis Technical Manual), and an antiscalant at 2 to 5 mg/L of feed as product (Hydranautics TAB-111).
A boiler receives its oxygen scavenger in the feedwater and its neutralizing amine where it reaches the steam.
The sequence from intake to distribution, stage by stage, is walked through with the chemicals it uses on the water treatment process page.
16 Types of Water Treatment Chemicals by Function#
The 16 types of water treatment chemicals by function are coagulants, flocculants, scale inhibitors, phosphates, corrosion inhibitors, oxygen scavengers, neutralizing amines, non-oxidizing biocides, oxidants, pH adjustment chemicals, dechlorination chemicals, chelating agents, defoamers, descaling and cleaning chemicals, ion exchange resins, and adsorbents and filter media. Of the 124 chemicals and media with their own page, 115 belong to these 16 families and 9 sit under 4 treatment programs (fluoridation, sulfide control, metal removal and nitrogen removal).
Table 1 compares the 16 families by job, main chemicals, main systems, number of chemical pages and one key number with its basis (mg/L = ppm).
| # | Family | What it does | Main chemicals | Main systems | Chemical pages | Key number with basis |
|---|---|---|---|---|---|---|
| 1 | coagulants for water treatment | destabilize particles, color and organic matter; precipitate phosphorus | alum, ferric chloride, PAC, ACH, polyDADMAC | drinking water, wastewater | 13 | 0.50 mg/L alkalinity as CaCO3 consumed per mg/L dry alum |
| 2 | flocculants for water treatment | bridge floc; condition sludge | polyacrylamide (anionic, cationic, nonionic) | drinking water, wastewater, sludge | 1 (+4 class pages) | 0.05 to 0.3 mg/L as coagulation aid in drinking water (NHMRC ADWG) |
| 3 | scale inhibitors | hold salts above saturation | HEDP, ATMP, PBTC, polyacrylates | cooling, RO, boilers | 11 | HEDP 2 to 5 mg/L as active in recirculating cooling |
| 4 | phosphates in water treatment | lead and copper control, sequestration, boiler hardness | phosphoric acid, zinc orthophosphate, SHMP, TSP | drinking water, boilers | 7 | at least 0.5 or 1.0 mg/L as PO4 in tap samples (LCRI) |
| 5 | corrosion inhibitors for water treatment | slow metal loss | molybdate, nitrite, zinc, azoles | cooling, closed loops | 8 | molybdate 200 to 300 mg/L as MoO4 in closed loops |
| 6 | oxygen scavengers for boiler water | remove dissolved oxygen | sodium sulfite, carbohydrazide, DEHA, hydrazine | boilers | 7 | 7.88 mg/L sodium sulfite per mg/L O2 (theoretical) |
| 7 | neutralizing amines for condensate treatment | neutralize carbonic acid in condensate | cyclohexylamine, morpholine, DEAE | steam and condensate | 6 | 2.0 to 2.6 ppm amine per ppm CO2 |
| 8 | biocides for water treatment | kill bacteria, algae and biofilm (non-oxidizing) | isothiazolinone, glutaraldehyde, DBNPA, quats | cooling, closed loops, RO | 11 | at least 4 h contact, 2 mechanisms alternated (HSG274) |
| 9 | oxidants and oxidizing biocides | disinfect and oxidize | chlorine, hypochlorite, ClO2, chloramine, ozone, peracetic acid | drinking water, wastewater, cooling | 17 | MRDL 4.0 mg/L as Cl2 (chlorine, chloramines) |
| 10 | pH adjustment chemicals | set pH and alkalinity | sodium hydroxide, lime, soda ash, sulfuric acid, CO2 | all systems | 10 | 1.25 mg/L alkalinity as CaCO3 added per mg/L NaOH |
| 11 | dechlorination chemicals | destroy residual chlorine | sodium bisulfite, SMBS, thiosulfate | wastewater, RO feed | 6 | 1.34 mg SMBS per mg Cl2 (theory), about 3.0 in practice |
| 12 | chelating agents in water treatment | complex hardness and iron | EDTA, GLDA, MGDA, gluconate | boilers, cleaning | 6 | 3.80 mg/L Na4EDTA per mg/L hardness as CaCO3 (active) |
| 13 | defoamers and antifoams | collapse foam | silicone, polyglycol, mineral oil | wastewater, evaporators, cooling | 0 (+4 class pages) | RO feed oil and grease at most 0.1 mg/L |
| 14 | descaling and chemical cleaning agents | dissolve scale and oxides | hydrochloric, sulfamic and citric acid | heat exchangers, boilers, membranes | 1 | 0.73 kg HCl (100 %) per kg CaCO3 dissolved |
| 15 | ion exchange resins for water treatment | soften, demineralize, remove selected ions | SAC, SBA, mixed-bed, selective resins | boilers, drinking water, process water | 0 (+8 class pages) | 1 eq/L = 21.8 kgr/ft3 as CaCO3 |
| 16 | adsorbents and filter media | filter and adsorb | GAC, PAC, anthracite, sand, greensand, activated alumina | drinking water, pretreatment | 11 | GAC10 = 10 min EBCT, reactivation every 180 days |
Chemical pages: 115 in the 16 families plus 9 under treatment programs (Table 6) make 124; the 39 class pages are linked from each family hub.
1. Coagulants#
Coagulants are positively charged chemicals that destabilize particles, color and natural organic matter so they form floc, such as alum, ferric chloride, polyaluminum chloride (PAC) and polyDADMAC. Metal coagulants consume alkalinity: 0.50 mg/L as CaCO3 per mg/L of dry alum and 0.92 mg/L per mg/L of ferric chloride. NSF/ANSI/CAN 60 maximum use levels (MULs) are product-specific, most commonly 150 mg/L for alum and 250 mg/L for PAC and ferric chloride, as product (NSF listings, 2026-10-20). The family spans 13 chemicals.
2. Flocculants#
Flocculants are high-molecular-weight polymers that bridge destabilized particles into large floc, such as anionic, cationic and nonionic polyacrylamide (PAM) of typically 1 to 20 million g/mol. Drinking water plants dose 0.05 to 0.3 mg/L as a coagulation aid (NHMRC Australian Drinking Water Guidelines), and 66 % of US surface-water plants use a polymer (EPA Six-Year Review 4, 2024). The residual acrylamide monomer is a treatment technique: 0.05 % monomer dosed at 1 ppm (40 CFR 141.111).
3. Scale inhibitors#
Scale inhibitors are threshold chemicals that hold calcium carbonate and other salts in solution above saturation, such as the phosphonates HEDP, ATMP and PBTC and polyacrylate polymers. Recirculating cooling water runs HEDP at 2 to 5 mg/L and PBTC at 3 to 5 mg/L as active (Standish, Water Technology, 2024). PBTC holds calcite at about 225 to 250 times saturation, against about 125 to 150 times for HEDP and ATMP. RO antiscalants are blends from the same chemistry.
4. Phosphates#
Phosphates are orthophosphate, polyphosphate and blended products that control lead and copper release, sequester iron and manganese and condition boiler hardness, such as phosphoric acid, zinc orthophosphate and sodium hexametaphosphate. EPA guidance (EPA 816-B-16-003) gives 1.0 to 3.0 mg/L as PO4 (0.33 to 1.0 mg/L as P) at pH 7.2 to 7.8. The LCRI requires at least 0.5 or 1.0 mg/L as PO4 in tap samples where orthophosphate is the treatment (40 CFR 141.82(f)(4)). Polyphosphate alone is not an effective lead inhibitor.
5. Corrosion inhibitors#
Corrosion inhibitors are chemicals that slow metal loss by forming a protective film, such as sodium molybdate, sodium nitrite, zinc salts and the azoles for copper. Closed loops run molybdate at 200 to 300 mg/L as MoO4 (120 to 180 mg/L as Mo) or nitrite at 600 to 1,200 mg/L as NO2 (Veolia Water Technologies Handbook, chapter 32). Chromate is banned in US comfort cooling towers, for use since 1990-05-18 (40 CFR 749.68).
6. Oxygen scavengers#
Oxygen scavengers are reducing chemicals that remove dissolved oxygen from boiler feedwater, such as sodium sulfite, carbohydrazide, DEHA and hydrazine. Sodium sulfite needs 7.88 mg/L per mg/L of oxygen in theory and suits boilers below 1,000 psig (69 bar); hydrazine or organic scavengers take over above that pressure (same handbook, chapter 11). Hydrazine carries the harmonised classification Carc. 1B (H350).
7. Neutralizing amines#
Neutralizing amines are volatile amines that travel with steam and neutralize carbonic acid in condensate, such as cyclohexylamine, morpholine and DEAE. Each ppm of CO2 needs 2.3 ppm of cyclohexylamine, 2.0 ppm of morpholine or 2.6 ppm of DEAE. Food-contact steam caps them at 10, 10 and 15 ppm in steam (21 CFR 173.310(d)).
8. Biocides (non-oxidizing)#
Non-oxidizing biocides are organic chemicals that kill bacteria, algae and biofilm by disrupting cell metabolism or membranes, such as isothiazolinone, glutaraldehyde, DBNPA and quaternary ammonium compounds. UK HSG274 Part 1 (2nd edition, 2024) describes contact times of typically at least 4 h and alternation of 2 biocides with different mechanisms. None of them is listed in 21 CFR 173.310.
9. Oxidants and oxidizing biocides#
Oxidants and oxidizing biocides are chemicals that disinfect and oxidize by accepting electrons, such as chlorine, sodium hypochlorite, chlorine dioxide, chloramine, ozone and peracetic acid. US maximum residual disinfectant levels (MRDLs) are 4.0 mg/L as Cl2 for chlorine and chloramines and 0.8 mg/L as ClO2 (40 CFR 141.65). Hypochlorous acid has a pKa of 7.54 at 25 °C (77 °F), so about half of free chlorine is HOCl at pH 7.5 and about 10 % at pH 8.5. Hypochlorite sold as 12.5 trade % holds 125 g/L of available chlorine (about 11.2 wt %).
10. pH adjustment chemicals#
pH adjustment chemicals are acids and alkalis that set pH and alkalinity, such as sodium hydroxide, hydrated lime, soda ash, sulfuric acid and carbon dioxide. Each mg/L of sodium hydroxide adds 1.25 mg/L of alkalinity as CaCO3, and each mg/L of sulfuric acid removes 1.02 mg/L (EPA OCCT guidance). The US secondary standard for pH is 6.5 to 8.5 (40 CFR 143.3), and discharges below pH 5.0 to a sewer are prohibited (40 CFR 403.5(b)(2)).
11. Dechlorination chemicals#
Dechlorination chemicals are reducing agents that destroy residual chlorine before discharge or ahead of membranes, such as sodium bisulfite, sodium metabisulfite (SMBS) and sodium thiosulfate. SMBS needs 1.34 mg per mg of chlorine in theory and about 3.0 mg in practice (DuPont FilmTec Reverse Osmosis Technical Manual). RO feed has to stay below 0.1 mg/L of free chlorine.
12. Chelating agents#
Chelating agents are chemicals that bind calcium, magnesium and iron into soluble complexes, such as EDTA, GLDA, MGDA and sodium gluconate. Stoichiometric demand is 3.80 mg/L of Na4EDTA per mg/L of hardness as CaCO3 (active basis). NSF/ANSI/CAN 60 has no listing category for EDTA, GLDA, MGDA, NTA or gluconate (NSF listings, 2026-10-20), so chelants serve boilers and off-line cleaning.
13. Defoamers and antifoams#
Defoamers and antifoams are surface-active chemicals that collapse and prevent foam, such as silicone emulsions, polyglycols and mineral-oil products. RO feed tolerates at most 0.1 mg/L of oil and grease, including silicone oil, per membrane manufacturer limits. Polyoxypropylene glycol is listed in 21 CFR 173.310, while silicones are not listed in 21 CFR 173.310. The family hub and its 4 class pages cover the products.
14. Descaling and cleaning chemicals#
Descaling and cleaning chemicals are acids and chelants that dissolve scale and oxides, such as hydrochloric, sulfamic and citric acid. Each kg of calcium carbonate needs 0.73 kg of HCl (100 %), about 2.3 kg of 32 % acid, 1.94 kg of sulfamic acid or 1.28 kg of citric acid. Sulfuric acid is never used to clean RO or NF membranes, because it precipitates calcium sulfate.
15. Ion exchange resins#
Ion exchange resins are polymer beads that swap ions to soften, demineralize or remove selected contaminants, such as strong acid cation (SAC), strong base anion (SBA), mixed-bed and selective resins. Resin capacity of 1 eq/L equals 21.8 kgr/ft3 as CaCO3, and a SAC softener regenerates with 90 to 240 g/L (5.6 to 15 lb/ft3) of NaCl in co-flow (the same manufacturer's ion exchange TechFact). Anion exchange is a best available technology for PFAS (40 CFR 141.61(d)), and resins are certified under NSF/ANSI/CAN 61.
16. Adsorbents and filter media#
Adsorbents and filter media are solids that strain particles or adsorb dissolved contaminants, such as granular and powdered activated carbon, anthracite, sand, greensand and activated alumina. US rules define GAC10 as a 10 min empty bed contact time (EBCT) with reactivation every 180 days (40 CFR 141.2). Powdered activated carbon carries product-specific NSF/ANSI/CAN 61 levels of 100, 250, 590 or 750 mg/L (NSF listings, 2026-10-20).
Top 10 Water Treatment Chemicals and What Each One Does#
The top 10 water treatment chemicals are aluminum sulfate, ferric chloride, polyaluminum chloride, zinc orthophosphate, chlorine, sodium hypochlorite, sodium hydroxide, ammonia, activated carbon and fluorosilicic acid, each on EPA's list of chemicals used in water treatment and each with a current AWWA B-standard. EPA keeps 47 supply-chain profiles, 36 of them for chemicals used in water treatment (page updated 2026-06-30), and AWWA publishes 49 B-standards. The list is a selection rule, not a volume ranking.
Volume figures exist for 3 of the 10. US alum production reached about 796 million kg in 2019, about 45 % of it for water; ferric chloride reached about 322 million kg, about 80 % for water (EPA supply-chain profiles). Municipal water uses about 628 million kg of chlorine per year.
Table 2 lists the 10 chemicals grouped in family order with their AWWA standard and one key number.
| # | Chemical | Family | Main job | AWWA standard | Key number |
|---|---|---|---|---|---|
| 1 | Aluminum sulfate (alum) | coagulants | coagulation, phosphorus removal | ANSI/AWWA B403-24 | US production about 796 million kg in 2019, about 45 % for water |
| 2 | Ferric chloride | coagulants | coagulation, phosphorus and sulfide control | ANSI/AWWA B407-24 | about 322 million kg in 2019, about 80 % for water; 0.92 mg/L alkalinity as CaCO3 consumed per mg/L |
| 3 | Polyaluminum chloride (PAC) | coagulants | coagulation with less alkalinity demand | ANSI/AWWA B408-25 | about 50 % basicity (medium grades); NSF/ANSI/CAN 60 MUL most commonly 250 mg/L as product |
| 4 | Zinc orthophosphate | phosphates | lead, copper and iron corrosion control | ANSI/AWWA B506-25 | NSF listing condition: zinc in finished water at most 2.0 mg/L |
| 5 | Chlorine (gas) | oxidants | primary and residual disinfection | ANSI/AWWA B301-24 | 628 million kg/yr to US municipal water; RMP threshold 2,500 lb (1,134 kg) |
| 6 | Sodium hypochlorite | oxidants | disinfection, oxidation | ANSI/AWWA B300-24 | 12.5 trade % = 125 g/L available chlorine; NSF MUL most commonly 84 mg/L as product |
| 7 | Sodium hydroxide (caustic soda) | pH adjusters | pH and alkalinity increase | ANSI/AWWA B501-25 | adds 1.25 mg/L alkalinity as CaCO3 per mg/L |
| 8 | Ammonia (anhydrous and aqueous) | pH adjusters (chloramination use) | chloramine formation | ANSI/AWWA B305-22 and B306-22 | Cl2:NH3-N weight ratio 4.5:1 to 5:1; NSF MUL 5 mg/L anhydrous |
| 9 | Activated carbon (PAC and GAC) | media | taste and odor, organics, PFAS | ANSI/AWWA B600-24 (PAC), B604-18 (GAC) | NSF/ANSI/CAN 61 PAC levels 100, 250, 590 or 750 mg/L; GAC10 = 10 min EBCT |
| 10 | Fluorosilicic acid | fluoridation (program) | community water fluoridation | ANSI/AWWA B703-24 | US optimal 0.7 mg/L fluoride (PHS 2015); NSF MUL 5 mg/L as product for most listings |
Selection rule: on EPA's list of 36 chemicals used in water treatment (profiles updated 2026-06-30) and covered by a current AWWA B-standard (AWWA list, 2026-10-20). Not a volume ranking.
Industrial programs rely on chemicals that EPA does not profile, such as phosphonates, oxygen scavengers, neutralizing amines and non-oxidizing biocides. Their importance shows in Table 3 by system, not in a national list.
Water Treatment Chemicals by Application#
Water treatment chemicals group by application: cooling towers use scale inhibitors, corrosion inhibitors and biocides; boilers use phosphates, oxygen scavengers and amines; membranes use antiscalants and dechlorination chemicals; wastewater and drinking water plants use coagulants, oxidants and pH adjustment chemicals. Each system has one control number that sets the dose.
Table 3 compares the 7 application areas by failure mode, families used and the number that governs dosing.
| Application | What goes wrong | Families used | Control number |
|---|---|---|---|
| cooling tower water treatment | scale, corrosion, biofouling, Legionella | scale inhibitors, corrosion inhibitors, biocides, oxidants, pH adjusters | blowdown = E / (C - 1); E about 1 % of recirculation per 10 °F (5.6 °C) of range |
| boiler water treatment | oxygen pitting, scale, condensate corrosion | phosphates, oxygen scavengers, amines, chelants, ion exchange | feedwater hardness 0.300 mg/L as CaCO3 at 0 to 450 psig (0 to 31 bar); not detectable above 1,000 psig (69 bar) |
| reverse osmosis and membrane chemicals | scaling, chlorine attack, fouling | scale inhibitors, dechlorination, biocides, cleaners | free chlorine below 0.1 mg/L; antiscalant 2 to 5 mg/L as product |
| wastewater treatment chemicals | solids, phosphorus, sulfide, foam, pathogens | coagulants, flocculants, oxidants, pH adjusters, dechlorination, defoamers | secondary BOD5 30 mg/L (30-day), pH 6.0 to 9.0 |
| drinking water treatment chemicals | turbidity, pathogens, DBPs, lead release | coagulants, flocculants, phosphates, oxidants, pH adjusters, media | TTHM 0.080 and HAA5 0.060 mg/L (LRAA); lead action level 0.010 mg/L from 2027-11-01 |
| closed loop water treatment | corrosion, microbes, glycol breakdown | corrosion inhibitors, biocides, pH adjusters | carbon steel at or below 0.2 mpy (0.005 mm/y) = excellent; glycol at least 25 % |
| produced water treatment chemicals | oil, solids, H2S, scale | scale inhibitors, biocides, coagulants | offshore oil and grease 42 mg/L daily max, 29 mg/L 30-day average (40 CFR 435.13) |
Industrial water treatment chemicals: cooling towers, boilers, membranes and closed loops#
Industrial water treatment chemicals protect equipment: cooling programs control the blowdown set by E / (C - 1), boiler programs remove oxygen and hardness, membrane programs stop scale and chlorine attack, and closed-loop programs hold corrosion rates down. Evaporation in a cooling tower runs at about 1 % of the recirculation rate per 10 °F (5.6 °C) of range (Veolia Water Technologies Handbook, chapter 31), so cycles of concentration decide how much scale inhibitor stays in the system. Boiler feedwater hardness limits fall from 0.300 mg/L as CaCO3 at 0 to 450 psig (0 to 31 bar) to not detectable above 1,000 psig (69 bar) under the ASME consensus guidelines.
Membrane plants keep free chlorine below 0.1 mg/L and dose antiscalant at 2 to 5 mg/L as product. Closed loops rate carbon steel corrosion at or below 0.2 mpy (0.005 mm/y) as excellent and need at least 25 % inhibited glycol where glycol is used (ChemAqua glycol guideline). Produced water discharged offshore meets 42 mg/L oil and grease as a daily maximum (40 CFR 435.13). How these programs are designed and costed, system by system, is compared under industrial water treatment chemical programs by application.
Municipal water treatment chemicals: wastewater and drinking water#
Municipal water treatment chemicals come from 5 core families: coagulants, flocculants, oxidants, pH adjustment chemicals and, in drinking water, phosphates and fluoride. The most common chemicals in wastewater treatment are metal coagulants for phosphorus and solids, polymers for sludge, chlorine or hypochlorite for disinfection and bisulfite for dechlorination. Secondary treatment has to reach BOD5 of 30 mg/L as a 30-day average and pH 6.0 to 9.0 (40 CFR 133.102), and chemical phosphorus removal uses a metal-to-phosphorus molar ratio of 1.5 to 2.0 for 80 to 98 % soluble phosphorus removal (EPA design manual).
Drinking water plants balance disinfection against byproducts: TTHM 0.080 mg/L and HAA5 0.060 mg/L as locational running annual averages (Stage 2 DBPR, 2006). The lead action level falls to 0.010 mg/L (90th percentile) from 2027-11-01 under the LCRI, which makes orthophosphate and pH control central. Fluoridation targets 0.7 mg/L fluoride (US PHS, 2015), well below the 4.0 mg/L MCL.
How Are Water Treatment Chemical Doses Stated and Calculated?#
Water treatment chemical doses are stated in mg/L (ppm) on a named basis, as product, as active or as an ion, and are converted to a feed rate with the flow and the product strength. The same 3 mg/L means different amounts of product on each basis, so a dose without its basis cannot be fed.
Dose basis: as product, as active or as an ion#
Every dose names its basis: 3 mg/L as PO4 is about 1 mg/L as P, and an NSF/ANSI/CAN 60 maximum use level is always stated as product, totaled across all application points. One percent equals 10,000 mg/L, and ppm equals mg/L only at a density of about 1. Hardness converts at 1 grain per US gallon = 17.1 mg/L as CaCO3. Operators should check the basis on the product data sheet before setting a pump.
Table 4 compares the 7 dose bases, what each measures and how to convert it.
| Basis | What it means | Example | Conversion |
|---|---|---|---|
| as product | weight of the commercial product per liter | NSF/ANSI/CAN 60 MUL; RO antiscalant 2 to 5 mg/L | product strength |
| as active | weight of the active ingredient | HEDP 2 to 5 mg/L in cooling | active % on the SDS |
| as CaCO3 | hardness and alkalinity on one scale | 0.50 mg/L alkalinity per mg/L alum | 1 gpg = 17.1 mg/L as CaCO3 |
| as PO4 / as P | orthophosphate | 1.0 to 3.0 mg/L as PO4 | as PO4 x 0.326 = as P |
| as Cl2 | available chlorine | MRDL 4.0 mg/L as Cl2 | 12.5 trade % = 125 g/L |
| as F | fluoride ion | 0.7 mg/L optimal | product per mg/L F on the fluoridation page |
| percent | concentration of a solution | 1 % | = 10,000 mg/L |
Chemical dosage: from mg/L to a feed rate#
Chemical dosage converts to a feed rate with lb/day = mg/L x MGD x 8.34 / purity, or kg/d = mg/L x m³/d / 1,000 / purity. The factor 8.34 is the weight in pounds of one US gallon of water, and purity is the active fraction as a decimal.
Worked example (sodium hypochlorite, inputs labelled):
- Flow: 10 MGD (37,854 m³/d).
- Dose: 2.0 mg/L as Cl2.
- Available chlorine needed: 2.0 x 10 x 8.34 = 166.8 lb/day (75.7 kg/d).
- Product: 12.5 trade % hypochlorite, 125 g/L available chlorine, 1.04 lb Cl2 per gallon.
- Product feed: 166.8 / 1.04 = about 160 gal/d (606 L/d).
The same arithmetic, with pump stroke and solution density added, is what the chemical dosage calculator converts mg/L into kg/d, lb/day, L/h and a pump setting with.
Which Standards and Regulations Govern Water Treatment Chemicals?#
Water treatment chemicals are governed in 4 layers: health certification (NSF/ANSI/CAN 60 and 61), product standards (AWWA and EN), residual limits in finished water and discharge, and rules for food-contact steam, biocides and chemical storage. Certification limits what a chemical adds to water, product standards fix its purity, and residual limits cap how much disinfectant or byproduct reaches the consumer.
Each layer has its own instrument and date, and the full set of US, Canadian and EU instruments is indexed under water treatment regulations and standards.
NSF/ANSI/CAN 60 and 61 certification#
NSF/ANSI/CAN 60 certification is required for drinking water treatment chemicals in the regulations of 48 of the 50 US states (NSF, 2019), and media and resins are certified under NSF/ANSI/CAN 61. A maximum use level is the highest product concentration allowed in finished water, totaled across every application point and stated as product. The listings hold 1,150 companies, 36,629 products and 54,847 product-function rows, with 250 mg/L the most frequent maximum use (NSF listings, 2026-10-21).
Certification is tied to the supply chain. It ends when a product is repackaged, diluted, transferred, blended or reacted after leaving the certified facility, so a distributor needs its own certification.
How maximum use levels are set and read is explained on NSF/ANSI/CAN 60.
AWWA and EN product standards#
AWWA publishes 49 B-series product standards for water treatment chemicals and media, from B100-25 to B703-24 (AWWA list, 2026-10-20), and CEN/TC 164 publishes the matching EN standards in Europe. Each AWWA B-series standards document sets purity, impurity limits, sampling and testing for one product, such as ANSI/AWWA B403-24 for aluminum sulfate.
The EN standards for drinking water treatment chemicals share one title pattern: "Chemicals used for treatment of water intended for human consumption" followed by the substance. Under the EU Drinking Water Directive 2020/2184, treatment chemicals and filter media fall under Article 12, while Article 11 covers materials in contact with water.
Residual limits that cap chemical doses#
Residual limits cap chemical doses through the MRDL of 4.0 mg/L as Cl2, TTHM 0.080 mg/L and HAA5 0.060 mg/L, the fluoride MCL of 4.0 mg/L and the treatment techniques for polymer monomers. None of these limits applies to the product itself; each applies to what the product leaves in finished water.
Table 5 compares US and EU limits on the residuals that water treatment chemicals add or form.
| Parameter | US value and instrument | EU value (Directive (EU) 2020/2184) | Chemicals it caps |
|---|---|---|---|
| Chlorine and chloramine residual | MRDL 4.0 mg/L as Cl2, running annual average (40 CFR 141.65) | n/a | hypochlorite, chlorine, ammonia |
| Chlorine dioxide residual | MRDL 0.8 mg/L as ClO2 (40 CFR 141.65) | n/a | ClO2, sodium chlorite |
| Chlorite / chlorate | chlorite MCL 1.0 mg/L; no chlorate MCL (40 CFR 141.64) | 0.25 mg/L each; 0.70 mg/L where ClO2 is used (from 2026-01-12) | ClO2, hypochlorite |
| TTHM / HAA5 | 0.080 / 0.060 mg/L LRAA (40 CFR 141.64) | THM 100 µg/L; HAA5 60 µg/L | oxidants (precursor control by coagulants, GAC) |
| Bromate | 0.010 mg/L (40 CFR 141.64) | 10 µg/L | ozone |
| Fluoride | MCL 4.0 mg/L; SMCL 2.0 mg/L; PHS optimal 0.7 mg/L is not a limit | 1.5 mg/L | fluorosilicic acid, sodium fluoride |
| Lead | action level 0.010 mg/L (90th percentile) from 2027-11-01, 0.015 mg/L until then (LCRI, 89 FR 86418, 2024-10-30) | 10 µg/L until 2036-01-12, then 5 µg/L | orthophosphate, pH adjusters |
| Copper | action level 1.3 mg/L (SMCL 1.0 mg/L) | 2.0 mg/L | orthophosphate, copper sulfate |
| Aluminum | SMCL 0.05 to 0.2 mg/L, non-enforceable; NSF listing condition 2 mg/L | 200 µg/L (indicator) | aluminum coagulants |
| Acrylamide / epichlorohydrin | treatment technique: 0.05 % at 1 ppm / 0.01 % at 20 ppm (40 CFR 141.111) | 0.10 µg/L each | polyacrylamide, polyamine |
| PFOA and PFOS | MCL 4.0 ng/L each, compliance 2029-04-26 (89 FR 32532); 2026-05 proposals pending | PFAS sum 0.10 µg/L | GAC, anion exchange (removal) |
EU values come from Directive (EU) 2020/2184 Annex I.
Rules for food-contact steam, biocides and chemical storage#
Food-contact steam, biocides and chemical storage fall under 4 further rules: 21 CFR 173.310 for boiler additives, FIFRA and the EU Biocidal Products Regulation for biocides, and EPA RMP and OSHA PSM for stored quantities. Under 21 CFR 173.310, only listed chemicals may enter steam that contacts food; cyclohexylamine and morpholine are capped at 10 ppm and DEAE at 15 ppm in steam, and an unlisted chemical carries only "not listed in 21 CFR 173.310".
The EU approves sodium hypochlorite as an active chlorine biocide for PT1 to PT5 (Regulation (EU) 2017/1273, 2019-01-01 to 2028-12-31), with drinking water disinfection under PT5. Stored chlorine triggers EPA RMP and OSHA PSM duties at different thresholds: 2,500 lb (1,134 kg) under the Risk Management Program (40 CFR 68.130) and 1,500 lb (680 kg) under Process Safety Management (29 CFR 1910.119). EPA's RMP proposal of 2026-02-24 is not final.
Complete List of Water Treatment Chemicals: All 124 Chemicals and Media#
The complete list holds 124 water treatment chemicals and media: 115 in the 16 families and 9 under 4 treatment programs. The list covers 34 of the 36 chemicals on EPA's in-use list with their own page; the other 2 appear as table rows or context.
Table 6 lists all 124 chemicals and media by family and program, in Table 1 order.
| # | Family or program | Pages | Chemicals and media |
|---|---|---|---|
| 1 | coagulants | 13 | Polyaluminum chloride (PAC); Aluminum Sulfate (Alum); Sodium Aluminate; PolyDADMAC; Aluminum Chlorohydrate (ACH); Ferric Chloride; Ferric Sulfate; Polyamine (Epi-DMA) Coagulant; Ferrous Sulfate; Aluminum Chloride Solution; Tannin (Quebracho Extract); Bentonite (Coagulant Aid); Ferrous Chloride |
| 2 | flocculants | 1 | Polyacrylamide (PAM) |
| 3 | scale inhibitors | 11 | HEDP (Etidronic Acid); PBTC (Phosphonobutane Tricarboxylic Acid); ATMP (Aminotris(methylenephosphonic acid)); DTPMP; Polymaleic Acid (HPMA); Polyaspartic Acid (PASP); Polyepoxysuccinic Acid (PESA); HPAA (Hydroxyphosphonoacetic Acid); Polyacrylic Acid and Sodium Polyacrylate; AA/AMPS Copolymer; Phosphinocarboxylic Acid (PCA) |
| 4 | phosphates | 7 | Sodium Hexametaphosphate (SHMP); Trisodium Phosphate (TSP); Phosphoric Acid; Zinc Orthophosphate; Monosodium Phosphate (MSP); Disodium Phosphate; Sodium Tripolyphosphate (STPP) |
| 5 | corrosion inhibitors | 8 | Sodium Molybdate; Benzotriazole (BZT); Sodium Nitrite; Sodium Silicate; Zinc Salts (Zinc Sulfate, Zinc Chloride); Tolyltriazole (TTA); Mercaptobenzothiazole (MBT); Octadecylamine (ODA) |
| 6 | oxygen scavengers | 7 | Carbohydrazide; DEHA (Diethylhydroxylamine); Hydrazine; Sodium Sulfite; Sodium Erythorbate; Hydroquinone; MEKO (Methyl Ethyl Ketoxime) |
| 7 | neutralizing amines | 6 | Morpholine; Cyclohexylamine; DEAE (Diethylaminoethanol); MOPA (Methoxypropylamine); AMP (2-Amino-2-methyl-1-propanol); Ethanolamine (ETA/MEA) |
| 8 | biocides | 11 | Isothiazolinone (CMIT/MIT); Glutaraldehyde; DBNPA; Quaternary Ammonium Compounds (ADBAC, DDAC); THPS (Tetrakis(hydroxymethyl)phosphonium Sulfate); Copper Sulfate (Reservoir Algaecide); Bronopol; TTPC (Tributyl Tetradecyl Phosphonium Chloride); Polyquaternium Algaecide (WSCP); Dodecylguanidine Hydrochloride (DGH); Methylene Bis(thiocyanate) |
| 9 | oxidants and oxidizing biocides | 17 | Peracetic Acid (PAA); Ozone; Monochloramine; Potassium Permanganate; Sodium Hypochlorite; Chlorine Dioxide; Hydrogen Peroxide; Calcium Hypochlorite; Chlorine Gas; Sodium Chlorite; Sodium Permanganate; Ammonium Sulfate (Chloramination); Oxygen (LOX); BCDMH (Bromochlorodimethylhydantoin); Trichloroisocyanuric Acid (TCCA) Tablets; Sodium Bromide (Activated Bromine); Sodium Chlorate |
| 10 | pH adjustment chemicals | 10 | Sodium Hydroxide (Caustic Soda); Hydrated Lime (Calcium Hydroxide); Soda Ash (Sodium Carbonate); Sulfuric Acid; Sodium Bicarbonate; Magnesium Hydroxide; Carbon Dioxide (CO2); Hydrochloric Acid; Quicklime (Calcium Oxide); Ammonia (Aqueous and Anhydrous) |
| 11 | dechlorination chemicals | 6 | Sodium Thiosulfate; Sodium Bisulfite; Sodium Metabisulfite (SMBS); Sulfur Dioxide; Ascorbic Acid (Vitamin C) Dechlorination; Calcium Thiosulfate |
| 12 | chelating agents | 6 | EDTA; Citric Acid; Sodium Gluconate; GLDA; MGDA; NTA (Nitrilotriacetic Acid) |
| 13 | defoamers and antifoams | 0 | no chemical pages; silicone, non-silicone, wastewater and evaporator classes are covered on the family hub and its 4 class pages |
| 14 | descaling and cleaning agents | 1 | Sulfamic Acid |
| 15 | ion exchange resins | 0 | no chemical pages; cation, anion, mixed-bed, softening, regeneration, demineralization, selective and dealkalization resins are covered on the family hub and its 8 class pages |
| 16 | adsorbents and filter media | 11 | Powdered Activated Carbon (PAC); Zeolite (Clinoptilolite); Calcite (Calcium Carbonate) Media; Granular Activated Carbon (GAC); Manganese Greensand; Anthracite Filter Media; Manganese Dioxide Media (Pyrolusite); Silica Filter Sand and Garnet; Activated Alumina; Diatomaceous Earth (Precoat Filter Media); Granular Ferric Hydroxide (GFH) |
| 17 | water fluoridation chemicals | 3 | Fluorosilicic Acid (FSA); Sodium Fluorosilicate; Sodium Fluoride (Water Fluoridation) |
| 18 | hydrogen sulfide and odor control chemicals | 2 | Triazine H2S Scavenger; Calcium Nitrate (Septicity and H2S Control) |
| 19 | heavy metal removal from wastewater | 3 | Sodium Sulfide and Sodium Hydrosulfide; TMT (Trimercapto-s-triazine); Dithiocarbamate Metal Precipitants |
| 20 | chemical support for nitrogen removal | 1 | Methanol (Denitrification Carbon Source) |
Totals: 115 in families plus 9 under programs make 124.
Each chemical's CAS number, function and NSF/ANSI/CAN 60 status sits in one sortable table, and every entry is filterable in the water treatment chemical database.
Who Supplies Water Treatment Chemicals and Treatment Programs?#
Water treatment chemicals reach a plant by 2 routes: a program provider who supplies, doses and monitors a treatment program, or a chemical supplier who delivers a product to the buyer's specification. Grand View Research put the global market at USD 35.8 billion in 2025, with coagulants and flocculants at 38.2 % of revenue and municipal users at 43.1 % of end use. The water treatment chemicals market figures are an analyst estimate, not a census.
Supply security shapes buying. EPA keeps 47 supply-chain profiles (updated 2026-06-30) because outages hit utilities directly: Winter Storm Uri took about 28 % of US chlor-alkali capacity offline in February 2021. Sodium hypochlorite degrades in storage, so plants take delivery of no more than about one month's supply at a time. Distributors and manufacturers by region are listed under water treatment chemical suppliers.
Certification follows the product through that chain. An NSF/ANSI/CAN 60 certificate ends when a product is repackaged or diluted after leaving the certified facility, so a buyer checks the listing of the company that delivers.
Program providers bundle chemicals with service, testing and reporting, and how to compare providers and quotes is covered under water treatment companies.
Are Water Treatment Chemicals Safe to Handle and to Drink?#
Water treatment chemicals are safe in finished water at or below their NSF/ANSI/CAN 60 maximum use levels and the residual limits, but the concentrates are corrosive, oxidizing or toxic as their safety data sheets state. Sodium hypochlorite carries the harmonised classification H314, H318, H400 and H410 (CLP Annex VI). Hydrazine is a Carc. 1B carcinogen (H350). Handling rules come from the supplier SDS and the regulator, never from a general guide.
What chemical is used to treat drinking water?#
Drinking water is treated with chemicals from 5 groups: coagulants such as alum and ferric chloride, disinfectants such as chlorine and sodium hypochlorite, pH adjusters such as caustic soda and lime, corrosion inhibitors such as orthophosphate, and fluoride compounds such as fluorosilicic acid. Fluoridation aims at 0.7 mg/L fluoride (US PHS, 2015). Polymers join the list at 66 % of US surface-water plants.
What are five common chemicals used for water disinfection?#
Five common chemicals used for water disinfection are chlorine, sodium hypochlorite, chloramine, chlorine dioxide and ozone. How they rank as primary and secondary disinfectants is compared under drinking water disinfection. Their strength differs widely: for 3-log Giardia inactivation at 10 °C (50 °F), the CT values are 112 mg·min/L for free chlorine (1.0 mg/L, pH 7.0), 1,850 for chloramines, 23 for chlorine dioxide and 1.43 for ozone (40 CFR 141.74). Hypochlorite shares the chlorine value, since both deliver free chlorine.
Which water treatment chemicals must never be mixed?#
Sodium hypochlorite must never be mixed with acids or acidic coagulants, because the mixture releases chlorine gas. Of 72 chemical unloading accidents recorded from 1953 to 2019, hypochlorite with hydrochloric acid caused 24 % and hypochlorite with ferric chloride 13 % (Chemical Engineering Transactions). The full matrix of incompatible pairs is set out under water treatment chemical compatibility and incompatible mixtures.
Is sodium metabisulfite used in water treatment?#
Yes, sodium metabisulfite (SMBS) is used in water treatment to remove residual chlorine ahead of RO membranes and before wastewater discharge. It needs 1.34 mg per mg of chlorine in theory and about 3.0 mg in practice. NSF/ANSI/CAN 60 maximum use levels run from 10 to 50 mg/L, most commonly 15 mg/L as product (NSF listings, 2026-10-20), and ANSI/AWWA B601-25 covers the product.
Which uses of these chemicals does this reference leave out?#
This reference leaves out 10 uses of the same chemicals: swimming pool, spa, pond, aquarium, household, emergency, medical, food, cosmetic and agricultural uses. It covers only chemicals and media dosed or specified to treat water in industrial, municipal and utility systems.