Caustic soda (sodium hydroxide, NaOH; CAS 1310-73-2) is the inorganic strong base that water treatment plants dose to raise pH and alkalinity, adding 1.25 mg/L of alkalinity as CaCO3 for every mg/L fed as NaOH (EPA, 2016).
Most plants buy 50 % liquid at 1.52 g/mL, and the most frequent NSF/ANSI/CAN 60 maximum use level is 100 mg/L as product, about 50 mg/L as NaOH (NSF listings, 2026-10-21). Caustic soda is one of the alkalis in this reference of water treatment chemicals.
Below: forms, mechanism, 5 water systems, dose arithmetic, freezing and steel limits, ANSI/AWWA B501-25 and EN 896, dated pH rules, harmonised H314, alternatives and bid prices.
The identity card below summarizes caustic soda.
| Attribute | Value |
|---|---|
| Names | Sodium hydroxide; caustic soda, caustic, lye, soda lye, sodium hydrate, liquid caustic; membrane-grade and diaphragm-grade caustic |
| Formula and molar mass | NaOH, 39.997 g/mol |
| CAS number | 1310-73-2 |
| EC number | 215-185-5 |
| Class | Inorganic strong base (alkali metal hydroxide) |
| Functions | pH adjuster, alkalinity source, neutralizer, anion resin regenerant, boiler alkalinity, corrosion control |
| Common delivered form | 50 % liquid, 1.52 g/mL at 20 °C (68 °F) |
| NSF/ANSI/CAN 60 | Product-specific MUL; 100 mg/L as product most frequent (NSF listings, 2026-10-21) |
| AWWA and EN standards | ANSI/AWWA B501-25; EN 896 |
| GHS | Harmonised CLP Annex VI (index 011-002-00-6): H314; Danger |
| Transport and customs | UN1824 (solution) and UN1823 (solid), class 8; HS 2815.12 (aqueous), US HTS 2815.12.00.00 |
Every value is checked against primary sources; see our methodology and fact-checking process.
What Is Sodium Hydroxide (Caustic Soda)?#
Sodium hydroxide is an inorganic strong base and the alkali that water treatment uses most often to raise pH and alkalinity.
Caustic soda is one of the 36 chemicals on the EPA list of water treatment chemical supply chain profiles. NSF listings carry trade names such as Alka-Trete and ACCO Hydrox 50-L.
Liquid, flakes or pellets: which caustic soda forms and strengths are supplied?#
Caustic soda is supplied as 50 % liquid, the most common bulk strength, as 25 % and other dilute liquids, and as 98 to 99 % solid flakes, pearls and beads. The 4 forms are listed below.
- 50 % liquid: membrane grade below 100 ppm NaCl, diaphragm grade below 1.1 % NaCl; 1.52 g/mL at 20 °C (68 °F).
- 25 % liquid: chosen to avoid freezing.
- Dilute liquids: 20 %, 30 to 33 %, 10 % and 5 % NaOH.
- Solids: deliquescent flakes, pearls and beads; density 2.1 g/cm³, pearl bulk density 1.2 kg/dm³ (EN 896).
Liquids are clear and colorless, at about pH 14.
How Does Caustic Soda Raise pH and Alkalinity?#
Caustic soda raises pH by dissociating fully, and its hydroxide converts CO2 and bicarbonate into carbonate. Each mg/L of NaOH adds 1.25 mg/L of alkalinity as CaCO3 without dissolved inorganic carbon (DIC), per the EPA Optimal Corrosion Control Treatment guidance (2016); 0.80 mg/L of NaOH supplies 1 mg/L as CaCO3.
Caustic soda reaches pH 14 at 25 °C and reacts faster than lime, soda ash or magnesium hydroxide (National Lime Association). P and M alkalinity measurement is described under alkalinity of water.
Why is caustic soda hard to control in poorly buffered water?#
Caustic soda adds hydroxide but no carbonate (DIC), so in poorly buffered water small dose changes move pH sharply. The EPA OCCT guidance advises against holding pH at 8.2 to 8.5, the weakest buffering zone. Utilities needing buffer target 5 to 10 mg C/L of DIC, supplied by soda ash (0.11 mg C/L per mg/L) or sodium bicarbonate (0.14 mg C/L per mg/L).
Where Is Caustic Soda Used in Water Treatment?#
Caustic soda is used in 5 water systems: drinking water, industrial wastewater, ion-exchange demineralizers, boilers and membrane cleaning. The table below compares dose basis, feed point, control and target in each system.
| System | Dose and basis | Feed point | Control | Target | Source |
|---|---|---|---|---|---|
| Drinking water: corrosion control and enhanced coagulation and TOC removal | To target pH; product MULs equal about 50 mg/L as NaOH | Post-filtration or clearwell; rapid mix for coagulation | Online pH, M alkalinity | Lead control pH 8.8 to 10; State minimum pH 7.0 | EPA OCCT 2016; 40 CFR 141.82(f) |
| Industrial wastewater: wastewater pH neutralization | 0.816 lb NaOH per lb H2SO4; 1.097 lb per lb HCl (stoichiometric) | Staged neutralization tanks | pH controller | Discharge pH 6.0 to 9.0 typical; never below 5.0 to a POTW | NLA |
| Sewers: hydrogen sulfide and odor control chemicals | Caustic shock dosing | Sewer line | pH | pH 12.5 held 20 min (one utility's practice) | EPA, Los Angeles practice |
| Demineralizers: ion exchange resin regeneration | 4 % NaOH, 75 to 160 g/L resin (co-flow) | Strong base anion resin | Regenerant strength and temperature | About 49 °C (120 °F) for silica | Veolia Water Handbook; DuPont TechFact |
| Boilers: hydroxide alkalinity and boiler corrosion | To the boiler-water hydroxide target | Internal treatment | P and OH alkalinity | Avoid concentration under deposits | Veolia Water Handbook |
| RO/NF cleaning (CIP) | 0.1 wt % NaOH, alone or with 1.0 % Na4EDTA or 0.025 % SDS; 0.1 % = 0.38 kg (0.83 lb) solid or 0.49 L (0.13 gal) of 50 % per 379 L (100 US gal) | Cleaning tank | pH | pH 12 at 35 °C (95 °F) max; pH 11.5 at 30 °C (86 °F) | DuPont FilmTec; Hydranautics |
| UF: ultrafiltration and MBR membrane cleaning chemicals | CEB 0.05 % NaOH with 0.1 % NaOCl; CIP 0.1 % NaOH with 0.2 % NaOCl | Backwash water; CIP tank | pH | CEB pH 12 to 13; CIP pH 12.5; seawater CEB at most 2 mmol/L NaOH | DOW UF manual 2011; DuPont inge manual |
Drinking water: corrosion control and coagulation pH#
Utilities feed caustic soda after filtration to raise distribution pH for lead and copper control, with an EPA OCCT lead target of pH 8.8 to 10, or 9.0 and above with lead service lines and no inhibitor. Under 40 CFR 141.82(f), the State sets a minimum distribution pH of at least 7.0 unless infeasible. pH and orthophosphate programs are compared under corrosion control treatment for lead and copper.
At the rapid mix, caustic soda restores alkalinity consumed by the coagulant; the Irish EPA (Advice Note 15) adjusts coagulation pH with alkali or acid, never by overdosing coagulant.
Wastewater: acid neutralization and metal hydroxide precipitation#
Caustic soda neutralizes acidic wastewater at 0.816 lb per lb of sulfuric acid and 1.097 lb per lb of hydrochloric acid (stoichiometric, NLA), faster than any other common alkali. Plants dose in staged tanks under a pH controller and discharge at pH 6.0 to 9.0, never below pH 5.0 to a publicly owned treatment works (POTW).
The trade-off is high TDS and a gel-like hydroxide sludge. Theoretical NaOH demand is 1.26 kg per kg of copper, 1.36 for nickel and 1.22 for zinc (calculated; field demand is higher). Hydroxide and sulfide precipitation are compared under heavy metal removal from wastewater.
Demineralizers and boilers: anion resin regeneration and hydroxide alkalinity#
Demineralizers regenerate strong base anion resin with 4 % caustic soda heated to about 49 °C (120 °F) to elute silica (Veolia Water Handbook). Removal needs 2 equivalents of NaOH per equivalent of CO2 or SiO2.
In boilers, caustic soda sets hydroxide alkalinity, measured as P and OH alkalinity. Under porous deposits it concentrates to 100,000 ppm against 5 to 10 ppm in bulk water (same handbook), causing caustic gouging. IAPWS TGD4-11(2015) bounds phosphate treatment at trisodium phosphate plus 1 mg/kg NaOH, as set out under phosphate treatment programs for boilers.
Membranes: alkaline RO cleaning and UF backwash#
RO and NF elements are cleaned with 0.1 wt % caustic soda at pH 12 and no more than 35 °C (95 °F), alone or with 1.0 % Na4EDTA or 0.025 % SDS (DuPont FilmTec cleaning manual, Rev 13, 2026). UF systems pair caustic with hypochlorite in chemically enhanced backwash (CEB), always followed by an acid CEB; seawater CEB stays at or below 2 mmol/L NaOH. The acid and alkaline cleaning sequence is described under RO membrane cleaning chemicals.
How Is the Caustic Soda Dose Calculated and Fed?#
A 10 mg/L dose as NaOH at 10,000 m³/d (2.64 MGD) needs 100 kg/d (about 220 lb/day) of NaOH, which is 132 L/d (about 35 gal/d) of 50 % caustic soda at 1.52 g/mL (calculated). The worked example lists every input; lb/day = mg/L x MGD x 8.34 / purity.
| Worked example input or result | Value |
|---|---|
| Dose | 10 mg/L as NaOH |
| Flow | 10,000 m³/d (2.64 MGD) |
| NaOH needed | 100 kg/d (about 220 lb/day) as NaOH |
| Product (50 % liquid) | 200 kg/d (about 441 lb/day) as product |
| Product density and content | 1.52 g/mL; 760 g NaOH per L (6.34 lb/gal) |
| Product volume | 132 L/d (about 35 gal/d) |
| Alkalinity added | +12.5 mg/L as CaCO3 |
How do you convert a caustic dose between product, 100 % NaOH and alkalinity?#
Multiply a dose as product by the NaOH fraction to get the dose as NaOH, and by 1.25 to get alkalinity as CaCO3: 100 mg/L of 50 % caustic is 50 mg/L as NaOH and about 62.5 mg/L as CaCO3. NSF maximum use levels scale the same way: 100 mg/L for 50 %, 200 mg/L for 25 % and 1,000 mg/L for 5 % all equal about 50 mg/L as NaOH. The chemical dosage and feed rate calculator converts any caustic dose between these bases.
Which feed equipment and temperatures does 50 % caustic soda need?#
50 % caustic soda begins to crystallize at about 12 °C (54 °F), so plants heat or insulate tanks and lines, unload at 21 °C (70 °F) or above (OxyChem Caustic Soda Handbook), or buy 25 % caustic. Freezing bottoms out near -27 °C (-16.6 °F) at 18 %; supplier data put 25 % at -18 to -25.5 °C (-0.4 to -13.9 °F).
At 20 °C, 50 % caustic has about 79 mPa·s viscosity (Westlake data sheet). Dilution releases heat: 50 % at 43 °C (110 °F) diluted to 20 % with 21 °C (70 °F) water reaches 54 °C (130 °F). Pump types and wetted materials are covered under chemical dosing pumps.
How Is Caustic Soda Dosing Controlled? pH and Alkalinity Testing#
Plants control caustic soda with 4 measurements: online pH, M alkalinity titration, P and OH alkalinity in boilers, and pH checks during membrane cleaning. They are listed below.
- Online pH: drinking water and neutralization; lead targets of pH 8.8 to 10 avoid the 8.2 to 8.5 zone.
- M alkalinity titration: confirms the 1.25 mg/L as CaCO3 gain per mg/L NaOH.
- P and OH alkalinity: tracks boiler hydroxide alkalinity.
- Cleaning-solution pH: DuPont adds caustic when RO cleaning pH falls over 0.5 units.
Targets by system are compiled under pH in water treatment.
What Is Caustic Soda Incompatible With? Acids, Metals and Water#
Caustic soda is incompatible with acids, water in bulk, flammable liquids, organic halogens, nitromethane and metals such as aluminum, tin and zinc (NIOSH Pocket Guide). Mixing with acid releases heat, and contact with aluminum, zinc or brass releases hydrogen. Incompatible pairs across all dosed chemicals are tabulated under water treatment chemical compatibility.
Will caustic soda damage pipes?#
Yes for aluminum, copper, zinc, lead and brass, but carbon steel handles 50 % caustic at 27 to 38 °C (80 to 100 °F) and 304L or 316L stainless steel serves to 93 °C (200 °F). Above 49 °C (120 °F), carbon steel suffers accelerated corrosion and cracking (OxyChem Caustic Soda Handbook). PE, PP, PVC and CPVC serve within their temperature limits, and FRP only with a caustic-resistant barrier.
Which Standards Cover Sodium Hydroxide? NSF/ANSI/CAN 60, AWWA B501 and EN 896#
Three documents govern caustic soda for drinking water: NSF/ANSI/CAN 60 for health effects, ANSI/AWWA B501-25 for product quality in North America and EN 896 in Europe. The table compares their scope and status.
| Document | Scope | Edition and status | Key requirement |
|---|---|---|---|
| NSF/ANSI/CAN 60 | Health effects of drinking water treatment chemicals | Typical use level from NSF/ANSI/CAN 60-2020 Table 5.1 | TUL 100 mg/L; product MULs per listing, total of all feed points |
| ANSI/AWWA B501-25 | Sodium Hydroxide (Caustic Soda) | Current on the AWWA standards list (2026-10-20); supersedes B501-19 | Physical, chemical, sampling, testing, packaging and shipping requirements (values not reproduced here) |
| EN 896 | Sodium hydroxide for water intended for human consumption; see EN standards for drinking water treatment chemicals | CEN standard (CEN/TC 164) | Product requirements for drinking-water use; 50 % at 1.52 g/mL |
What is the NSF/ANSI/CAN 60 maximum use level for caustic soda?#
No single NSF/ANSI/CAN 60 limit exists for caustic soda: product MULs are stated as product, and 100 mg/L appears most often, mainly on 50 % liquid and solid grades (NSF listings, 2026-10-21). The listings hold 151 companies, 1,194 products and 2,777 product-function rows; 100 mg/L appears on 841 rows, 200 mg/L on 560, 250 mg/L on 229 and 165 mg/L on 96. The 100 mg/L typical use level in NSF/ANSI/CAN 60-2020 Table 5.1 is not a product MUL; each MUL is the total of all feed points.
Listings differ by facility: Univar's Caustic Soda 50% carries 200 mg/L at Thunder Bay but 100 mg/L at Abbotsford and Dartmouth (NSF listing, 2026-10-20). Certification to NSF/ANSI/CAN 60 is required in 49 US states (NSF survey of ASDWA members); MULs, TULs and listings are explained under NSF/ANSI/CAN 60 certification.
What do ANSI/AWWA B501-25 and EN 896 cover?#
ANSI/AWWA B501-25 Sodium Hydroxide (Caustic Soda) is the current AWWA edition and replaces B501-19, after the -13 and -08 editions. Like every AWWA B-standard, it sets physical, chemical, sampling, testing, packaging and shipping requirements. EN 896 is the matching CEN standard. B501 sits in the scale and corrosion control group of the AWWA B-series standards.
What Is the Regulatory Status of Caustic Soda in Water Treatment?#
Caustic soda is not a FIFRA pesticide and is listed in 21 CFR 173.310; its use is regulated through the pH it leaves in finished water and effluent (status 2026-10-20). The matrix below lists each instrument with its value.
| Instrument | Value | Type | Reference |
|---|---|---|---|
| NSF/ANSI/CAN 60 | 100 mg/L as product most frequent MUL | Certification | NSF listings, 2026-10-21 |
| US SMCL, Safe Drinking Water Act | pH 6.5 to 8.5 | Non-enforceable | 40 CFR 143.3 |
| Lead and copper rule | State minimum distribution pH 7.0 or higher unless infeasible | OCCT designation | 40 CFR 141.82(f) |
| EU Drinking Water Directive 2020/2184 | pH 6.5 to 9.5, water not aggressive; sodium indicator 200 mg/L | Indicator parameters | Annex I Part C |
| WHO guidelines for drinking-water quality | No health-based pH value; chlorination preferably below pH 8.0 | Guidance | WHO GDWQ |
| POTW effluent; national pretreatment program | Effluent pH 6.0 to 9.0; no discharge below pH 5.0 | Secondary treatment; prohibited discharge | 40 CFR 133.102(c); 40 CFR 403.5(b)(2) |
| RCRA corrosivity | D002 at pH 2 or below, or 12.5 or above | Hazardous waste characteristic | 40 CFR 261.22 |
| 21 CFR 173.310 boiler water additives | Listed; no limit beyond the functional amount | Food-contact steam | 21 CFR 173.310(c), eCFR 2026-09-01 |
| FIFRA | Not a pesticide | Status | EPA |
| EPA RMP and OSHA PSM | Not listed | Process safety | 40 CFR 68.130; 29 CFR 1910.119 App. A |
| OSHA and NIOSH | PEL TWA 2 mg/m³; REL ceiling 2 mg/m³; IDLH 10 mg/m³ | Exposure limits | NIOSH Pocket Guide |
Caustic soda's pH role beside disinfection and corrosion control is described under drinking water treatment chemicals.
Is spent caustic a corrosive hazardous waste?#
Yes when its pH is 12.5 or higher: such aqueous waste shows the RCRA corrosivity characteristic D002 under 40 CFR 261.22. Caustic soda as supplied has a pH of about 14, so spent regenerant and cleaning solutions are tested before discharge.
How Should Caustic Soda Be Handled and Stored Safely?#
Caustic soda at 5 % and above is harmonised Skin Corr. 1A, H314 (Danger), so plants store it in steel, stainless steel or compatible plastic tanks within temperature limits and follow the supplier SDS for PPE. The full Annex VI entry (index 011-002-00-6) is H314 with concentration limits: Skin Corr. 1A at 5 % or more, Skin Corr. 1B at 2 to below 5 %, and Skin Irrit. 2 (H315) and Eye Irrit. 2 (H319) at 0.5 to below 2 %.
Tanks keep 50 % caustic above about 12 °C (54 °F) and carbon steel below 49 °C (120 °F) (OxyChem). Personal protection, spill response and first aid follow the supplier SDS. Containment and sizing are covered under chemical storage tanks. The table summarizes storage values.
| Property | Value | Source |
|---|---|---|
| pH as supplied | About 14 | NLA |
| Classification | Harmonised H314, Danger, GHS05; Skin Corr. 1A at 5 % or more | CLP Annex VI, 011-002-00-6 |
| Exposure limits | OSHA PEL TWA 2 mg/m³; NIOSH REL ceiling 2 mg/m³; IDLH 10 mg/m³ | NIOSH Pocket Guide |
| Tank materials | Carbon steel 27 to 38 °C (80 to 100 °F); 304L/316L to 93 °C (200 °F); PE, PP, PVC, CPVC within limits | OxyChem |
| Incompatible | Acids, water in bulk, flammable liquids, organic halogens, Al, Sn, Zn, nitromethane | NIOSH |
| Freezing | 50 %: about 12 °C (54 °F); 18 %: about -27 °C (-16.6 °F); 25 %: -18 to -25.5 °C | OxyChem; Chlorine Institute; supplier data |
| Transport | UN1824 solution, class 8, PG II or III; UN1823 solid, class 8, PG II | 49 CFR 172.101 |
| Process safety | Not listed under EPA RMP or OSHA PSM | 40 CFR 68.130; 29 CFR 1910.119 |
What does a sodium hydroxide safety data sheet (SDS) cover?#
A sodium hydroxide safety data sheet (the older MSDS) gives classification, exposure limits, storage and transport data for one product, and the classification changes with strength. Run the 4 checks below.
- Confirm the strength on the SDS against the certificate of analysis.
- Check section 2 against harmonised H314 and the concentration limits for that strength.
- Check section 14 against UN1824 (solution) or UN1823 (solid), class 8.
- Check section 8 against the 2 mg/m³ OSHA PEL and NIOSH ceiling.
What Are the Alternatives to Caustic Soda?#
The 4 main alternatives are hydrated lime, soda ash, sodium bicarbonate and magnesium hydroxide, which differ in alkalinity per mg/L, carbonate added and maximum pH. The table compares them with caustic soda.
| Alkali | CAS | Alkalinity as CaCO3 per mg/L | DIC added | Max pH (25 °C) | NSF TUL 2020 | AWWA | 21 CFR 173.310 |
|---|---|---|---|---|---|---|---|
| Caustic soda | 1310-73-2 | 1.25 | None | 14 | 100 mg/L | B501-25 | Listed |
| Hydrated lime | 1305-62-0 | 1.35 | None | 12.45 | 650 mg/L | B202-25 | Not listed |
| Soda ash | 497-19-8 | 0.94 | 0.11 mg C/L per mg/L | Above 11 | 100 mg/L | B201-18 | Listed |
| Sodium bicarbonate | 144-55-8 | 0.60 | 0.14 mg C/L per mg/L | n/a | 100 mg/L | None | Not listed |
| Magnesium hydroxide | 1309-42-8 | 1.72 (calculated) | None | 10.6 | 150 mg/L | None | Not listed |
Caustic soda vs hydrated lime#
Hydrated lime adds slightly more alkalinity per mg/L than caustic soda (1.35 against 1.25 as CaCO3) but needs slurry or dry feed, while caustic soda feeds as a liquid and reacts fastest. Slurry feed and softening are covered under hydrated lime (calcium hydroxide).
Caustic soda vs soda ash and sodium bicarbonate#
Soda ash and sodium bicarbonate (baking soda) raise alkalinity more gently than caustic soda and add carbonate (DIC), which buffers pH; caustic soda adds none. DIC dosing is covered under soda ash (sodium carbonate).
Caustic soda vs magnesium hydroxide#
Magnesium hydroxide is self-buffering with a maximum pH of 10.6 and replaced caustic soda at 0.75 to 0.79 lb dry per lb dry NaOH in one published field trial. Slurry uses are covered under magnesium hydroxide.
Caustic Soda Grades, Suppliers and Sourcing#
Caustic soda is made by chlor-alkali producers and sold through distributors in membrane and diaphragm grades that differ in salt content (below 100 ppm against below 1.1 % NaCl). Salt matters for demineralizers: 2 % NaCl in caustic cuts anion regeneration efficiency by 5 to 10 %, so the DuPont AmberLite manual limits regenerant NaCl to 1.0 %. Producers and distributors by region are listed under water treatment chemical suppliers.
Olin's Form 10-K for fiscal 2025 names water treatment among the largest caustic soda end uses. The table lists makers and distributors.
| Company | Role |
|---|---|
| Allied Universal | Distributor |
| Brenntag | Distributor |
| Olin | Chlor-alkali producer |
| OxyChem | Chlor-alkali producer |
| Westlake | Chlor-alkali producer |
Listed alphabetically; no company is a partner of this site and none pays for inclusion. Buyers should check the NSF listing for both product and facility.
How is caustic soda priced and quoted?#
Utility bids price caustic soda on a dry NaOH basis, so a 50 % delivery is billed for the NaOH it contains (Fairfax Water: dry NaOH, 76 % Na2O basis, 3,000 to 4,000 gal loads). Liquid caustic ships under HS 2815.12 and solid under US HTS 2815.11.00.00.
Public procurement records show what buyers paid at a given date and place; they include delivery and local terms and are not a current price. The Bay Area Chemical Consortium in California received 2 bids of USD 689.5 to 1,515 per dry ton for 50 % sodium hydroxide, delivered by region (bid opening 2026-02-19, BACC Project 12-2026). Further tabulations, each from one document:
| Date | Region | Product | Range | Basis | Source |
|---|---|---|---|---|---|
| 2026-02-19 (bid opening) | Bay Area Chemical Consortium regions, California, US | 25 % NaOH, 2 bids | USD 820 to 1,420 | Per dry ton, delivered by region | BACC Project 12-2026 bid results |
| 2025-02-05 (bid opening) | Hanover Borough and Penn Township joint bid, Pennsylvania, US | 50 % liquid caustic in bulk, 2 bids | USD 0.1698 to 0.1735 | Per pound | Joint municipal bid tabulation, 2025 |
| 2024-06-11 (bid opening) | Texarkana, Arkansas, US | Caustic soda, bulk liquid, 4 bids | USD 0.2148 to 0.2400 | Per wet pound | FY 2024-2025 chemical bid tabulation |
| 2024-06-04 (bid opening) | Concord, North Carolina, US | 50 % NaOH, bulk, 5 bids | USD 637.00 to 948.00 | Per dry ton | Bid #2633 tabulation |
| 2024-06-04 (bid opening) | Concord, North Carolina, US | 25 % NaOH, bulk tanker, 4 bids | USD 1.092 to 1.36 | Per gallon | Bid #2633 tabulation |
Quotes depend on strength and basis, volume, container, freight, contract term and NSF/ANSI/CAN 60 certification. To compare offers on one dry-NaOH specification, request quotes for water treatment chemicals.
Where Does Caustic Soda Sit Among pH Adjustment Chemicals?#
Caustic soda is the strongest and fastest alkali among the 10 pH adjustment chemicals in this reference, beside acids such as sulfuric and hydrochloric acid that lower pH. All acids and alkalis are compared under pH adjustment chemicals for water treatment. Its acid counterpart for lowering pH, alkalinity and scale potential is sulfuric acid.
Caustic soda FAQs#
Does caustic soda raise or lower pH?#
Caustic soda raises pH. It dissociates fully into hydroxide ions and can lift water toward pH 14, the highest of the common alkalis.
Does caustic soda add sodium to drinking water?#
Yes, caustic soda adds sodium along with the hydroxide. The EU Drinking Water Directive 2020/2184 lists sodium as an indicator parameter with a value of 200 mg/L.
Does caustic soda remove silica from RO membranes?#
Caustic soda alone is the Hydranautics cleaning solution for polymerized silica on RO elements, dosed at 0.1 % and pH 11.5 at up to 30 °C (86 °F).
Silica limits are covered under silica scale in RO and cooling systems.
Is caustic soda listed for boiler steam that contacts food?#
Sodium hydroxide is listed in 21 CFR 173.310(c), with no limit beyond the amount needed for its function. The listing covers boiler water additives in steam that contacts food (eCFR text as of 2026-09-01).