Aluminum Sulfate (Alum) in Water Treatment: Uses, Dosage, Specifications and Safety

Aluminum sulfate (alum, also written aluminium sulphate; CAS 10043-01-3) is a monomeric aluminum salt coagulant for water treatment, sold mainly as liquid alum containing up to 48.5 % dry alum (Al2(SO4)3·14H2O) by weight. Because alum carries no basicity, every milligram consumes alkalinity.

Drinking-water plants dose 5 to 200 mg/L (ppm) as dry alum, and 150 mg/L as product is the most common NSF/ANSI/CAN 60 maximum use level (NSF listings, 2026-10-21). Alum is one of the coagulants in this reference of water treatment chemicals, each documented with the same identity, dose and compliance fields.

Three values decide most alum programs: the dose basis (1 mg/L of liquid alum is 0.485 mg/L of dry alum), the alkalinity demand (0.50 mg/L as CaCO3 per mg/L dry alum) and the residual aluminum value (0.05 to 2.9 mg/L by jurisdiction).

The identity card below summarizes the attributes that define aluminum sulfate.

Every value on this page is checked against primary sources (NSF listings, AWWA, CEN, EPA, Health Canada, WHO); see our methodology and fact-checking process.

What Is Aluminum Sulfate (Alum)?#

Aluminum sulfate is a monomeric aluminum salt with 0 % basicity, supplied for water treatment mainly as 48.5 % liquid alum, a solution whose strength is stated as dry alum equivalent (Al2(SO4)3·14H2O). The anhydrous salt, Al2(SO4)3, has a molar mass of 342.2 g/mol; the 14-hydrate that defines dry alum weighs 594.4 g/mol, so dry alum contains 17.2 % Al2O3 in theory.

Which strength does a buyer receive? The Australian Drinking Water Guidelines (NHMRC) give 7.5 to 8.4 % Al2O3 for liquid alum, equal to 43 to 50 % dry alum; the exact value appears on each certificate of analysis.

The table below compares alum forms and grades by strength, density, pH and freezing point.

Liquid or dry alum: which form is used where?#

Liquid alum (48.5 % dry alum equivalent, about 5.3 to 5.5 lb dry alum per US gallon or 0.63 to 0.65 kg/L) feeds neat from bulk storage, while dry alum (lump, granular or powder, about 17 % Al2O3) needs a dry feeder and a dissolving step. The "48 %" on liquid offers refers to the 14-hydrate, so 48.5 % liquid alum carries only about 8.3 % Al2O3.

Is potash alum the same as aluminum sulfate?#

No: potash alum is potassium aluminum sulfate, KAl(SO4)2·12H2O (CAS 10043-67-1; 12-hydrate CAS 7784-24-9, 474.4 g/mol), and it carries 5.69 % Al by weight against 9.08 % for dry alum. Equal aluminum therefore needs about 1.6 times the mass of potash alum (calculated). Potassium alum has no NSF/ANSI/CAN 60 chemical category, no AWWA or EN standard and no listing in 21 CFR 173.310.

How Does Aluminum Sulfate Work as a Coagulant?#

Aluminum sulfate coagulates by hydrolyzing to cationic aluminum hydroxo species and aluminum hydroxide, Al(OH)3: at low dose and slightly acidic pH the cations neutralize colloid charge, and at higher dose near neutral pH the precipitating hydroxide sweeps particles out as floc. The Australian Drinking Water Guidelines place enhanced coagulation at pH 5.5 to 6.2 and sweep coagulation at pH 6.5 to 7.5, and the Veolia water handbook gives an alum optimum of pH 6.0 to 7.0.

The overall reaction with bicarbonate alkalinity is Al2(SO4)3·14H2O + 3 Ca(HCO3)2 → 2 Al(OH)3 + 3 CaSO4 + 6 CO2 + 14 H2O. Flocculation then grows the destabilized particles into settleable floc. Rapid mix, floc growth and separation are explained under coagulation and flocculation in water treatment.

How much alkalinity does alum consume?#

Alum consumes 0.50 mg/L of alkalinity as CaCO3 per mg/L of dry alum (stoichiometric 300/594.4; the Hach table prints 0.49), so a 30 mg/L dose removes about 15 mg/L as CaCO3 (calculated). The 5.56 factor in some tables applies only to a dose stated as Al.

The table below lists what 1 mg/L of dry alum consumes, produces and delivers.

In low-alkalinity water, lime, caustic soda or soda ash may be needed to hold coagulation pH (ADWG). P and M alkalinity are measured as set out under alkalinity of water, and alkali feed for acidic effluents is covered under wastewater pH neutralization.

Where Is Alum Used? Drinking Water, Municipal and Industrial Wastewater#

Alum is used in 3 water systems: drinking water (turbidity, color and TOC removal), municipal wastewater (phosphorus removal and sludge conditioning) and industrial water and wastewater (raw-water clarification, softening support and color removal).

The table below compares alum use by system, with dose basis, feed point, control and target.

Drinking water: turbidity, color and enhanced coagulation#

Drinking-water plants dose 5 to 200 mg/L (ppm) as Al2(SO4)3·14H2O at the rapid mix, up to about 500 mg/L for very dirty water (ADWG), which equals about 0.45 to 18 mg/L as Al (calculated).

How much extra alum does TOC removal justify? Under 40 CFR 141.135, Step 2 jar testing adds alum in 10 mg/L increments until another 10 mg/L removes 0.3 mg/L of TOC or less, at target pH 5.5, 6.3, 7.0 or 7.5 by alkalinity band. Step 1 and Step 2 tables sit under enhanced coagulation and TOC removal. TOC removal limits the precursors of disinfection byproducts.

Does alum work in cold water?#

Yes, but less efficiently: coagulation efficiency declines with temperature, and some evidence shows alum more affected than iron salts below 5 °C (41 °F) (Irish EPA). Water at 0 °C (32 °F) is twice as viscous as at 25 °C (77 °F), and the optimum pH falls about 0.4 units between 2 and 20 °C (35.6 and 68 °F). One utility switches to polyaluminum chloride below 12 °C (54 °F).

Municipal wastewater: phosphorus removal and sludge conditioning#

Alum removes phosphorus at a stoichiometric 1:1 molar Al:P ratio, 0.87 mg Al or 9.6 mg dry alum per mg P (MPCA), which a supplier-authored WaterWorld article puts at about 20 mg/L of liquid alum per mg/L P. EPA's 1987 phosphorus design manual places the optimum at pH 5.5 to 6.5 and lists 10.3 mg/L as Al (raw wastewater) or 7.5 mg/L as Al (mixed liquor) for 1 mg/L effluent total phosphorus.

The same manual reports that aluminum precipitation raises sludge volume by 58 %, against 25 % for iron. That extra sludge is handled with sludge thickening and dewatering polymers. Aluminum, iron and lime programs are compared under chemical phosphorus removal from wastewater.

Industrial water and wastewater: clarification, softening and color#

Industrial plants use alum to clarify raw water and effluents; color coagulation with aluminum or iron salts runs at pH 4.5 to 5.5 (Veolia water handbook). In lime softening, alum converts carbonate to non-carbonate hardness, polymers are often preferred as coagulant aids, and soluble aluminum gives falsely low 2P-M readings.

Decolorants are compared under color removal from wastewater. For metalworking-fluid emulsions, one study found good separation at 0.75 to 1.0 mM Al3+ (about 20 to 27 mg/L as Al, calculated) and pH 6.0 to 7.5 (IntechOpen), a figure to confirm by jar test.

Coagulants by industry are listed under industrial wastewater treatment chemicals.

How Is the Alum Dose Calculated and Fed?#

The daily alum feed equals dose x flow: 30 mg/L as dry alum at 10 MGD (37,854 m³/d) is 2,502 lb/day (1,136 kg/d), about 1,760 L/d (465 gal/d) of 48.5 % liquid alum. The formulas are lb/day = mg/L x MGD x 8.34 / purity (Florida DEP) and kg/d = mg/L x m³/d / 1,000.

The worked example below labels every input; all results are calculated.

An EPA guidance example that converts 49 % liquid alum at specific gravity 1.2 to 588 g/L understates a standard liquid by about 9 %, so the certificate's specific gravity belongs in the calculation.

How do you convert an alum dose between liquid alum, dry alum, Al2O3 and Al?#

1 mg/L of liquid alum (48.5 %) equals 0.485 mg/L of dry alum, and 1 mg/L of dry alum equals 0.172 mg/L as Al2O3 or 0.091 mg/L as Al; per mg/L of liquid alum that is 0.083 mg/L as Al2O3 and 0.044 mg/L as Al (calculated).

A New Jersey AWWA operator course shows why the basis matters: 100 gpd of liquid alum (SG 1.33, 48.5 %, 9.5 % Al2O3) fed into 10 MGD is 13.3 ppm wet, 6.45 ppm as dry alum and 1.26 ppm as Al2O3. The dosage and feed rate calculator converts any alum dose and flow.

Which feed equipment and storage temperature does liquid alum need?#

Liquid alum is fed by metering pumps from rubber-lined, fiberglass, 316 stainless steel or plastic tanks kept indoors or heated, since standard liquid alum freezes at 9 °F (-12.8 °C) and acidified grades at 0 to 10 °F (-18 to -12 °C) (USALCO technical data). Liquid alum keeps about 36 months (EPA supply chain profile, 2022). Wetted materials and pump types are compared under chemical dosing pumps.

How Is Alum Coagulation Controlled? pH, Turbidity and Residual Aluminum#

Plants control alum coagulation with 5 measurements: jar tests, coagulation pH, settled and filtered turbidity, residual aluminum (total and dissolved) and alkalinity.

The 5 measurements and what each shows are listed below.

• Jar tests set the dose and pH window.
• Coagulation pH sits at 5.5 to 7.5 (ADWG).
• Combined filter effluent stays at or below 0.3 NTU in at least 95 % of monthly measurements, never above 1 NTU (40 CFR 141.173); Health Canada recommends a 0.1 NTU goal.
• Residual aluminum, total and dissolved, is monitored at least daily (Health Canada).
• Alkalinity shows whether the demand needs alkali support.

NTU, FNU and filter limits are explained under turbidity in water.

How do plants keep residual aluminum low with alum?#

Plants keep residual aluminum low by holding coagulation pH at 6.5 to 7.0 below 10 °C (50 °F) and at 6.0 to 6.5 in warmer water (Health Canada, 2021), because the minimum solubility of aluminum hydroxide moves from about pH 6.2 at 20 °C (68 °F) to about pH 6.7 at 5 °C (41 °F). Coagulation pH is corrected with acid or alkali, never by overdosing alum (Irish EPA).

Health Canada also recommends a distribution pH of at least 7.0 (±0.2). In a US survey cited by WHO (Miller et al., 1984), alum plants showed a median residual of 0.1 mg/L and a maximum of 2.7 mg/L.

How is alum dosed in a jar test?#

A jar test doses alum from a 20 g/L stock solution, so 1 mL in a 2 L jar equals 10 mg/L; the stock is no more than 7 days old and below pH 3.0 (EPA Step 2 guidance). Neat liquid alum needs about 15 µL for the same dose (µL = mg/L x jar liters / SG, at SG 1.33; calculated). Mixing speeds and reading the jars follow the jar test procedure.

What Is Aluminum Sulfate Incompatible With? Hypochlorite, Ferric Chloride and Fluoride#

Aluminum sulfate releases chlorine gas when mixed with sodium hypochlorite and reacts exothermically, with acid fumes, when mixed with ferric chloride (Minnesota Pollution Control Agency). Fill connections for these chemicals are never identical, unlabeled and side by side.

The 3 interactions to design around are listed below.

• Hypochlorite: alum and sodium hypochlorite never share fill lines, tanks or containment.
• Ferric chloride: the two react exothermically with acid fumes in one tank.
• Fluoride: about 30 % is lost when fed ahead of filtration at 100 mg/L alum, and alum interferes with the SPADNS method, so an ion-selective electrode is preferred.

Fluoride feed points after filtration are covered under water fluoridation chemicals.

Which Standards Cover Aluminum Sulfate? NSF/ANSI/CAN 60, AWWA B403 and EN 878#

Three documents govern aluminum sulfate for drinking water: NSF/ANSI/CAN 60 for health effects, ANSI/AWWA B403-24 for product quality in North America and EN 878:2016 in Europe.

The table below compares 4 documents by scope, edition and key requirement.

What is the NSF/ANSI/CAN 60 maximum use level for alum?#

No single NSF/ANSI/CAN 60 limit exists for alum: maximum use levels are product-specific, and 150 mg/L as product is the most common value (744 of 1,536 product-function rows), followed by 400 mg/L (382 rows) and 300 mg/L (176 rows), within a range of 25 to 500 mg/L (NSF listings, 2026-10-21). Some listings carry footnote [1], "maximum use based on dry basis", and copper-containing alum blends carry [CP]: copper in finished water is monitored so it does not exceed 1.3 mg/L.

The binding figure is the MUL of the purchased product from its facility, summed over all feed points; a Univar Canada 48 % alum is listed at 309 mg/L. MULs and their footnotes are covered under NSF/ANSI/CAN 60 certification.

The aluminum sulfate listings cover 113 companies, 464 products (company plus trade designation), 1,536 product-function rows and 272 facility entries (NSF listings, 2026-10-21). Certification is required in 49 US states (NSF survey of ASDWA members).

What do ANSI/AWWA B403-24 and EN 878:2016 cover?#

ANSI/AWWA B403-24, Aluminum Sulfate: Liquid, Ground, or Lump, is the current edition, replacing B403-16, and covers liquid alum containing up to 48.5 % by weight dry alum equivalent alongside ground and lump dry grades. It sets physical, chemical, sampling, testing, packaging and shipping requirements and sits beside B405 and B408 in the AWWA B-series standards.

EN 878:2016 is the European product standard for aluminum sulfate and supersedes EN 878:2004; EN 1302:2024 gives the analytical methods for aluminum-based coagulants.

What Is the Regulatory Status of Aluminum Sulfate in Drinking Water Treatment?#

Aluminum sulfate is not a pesticide under FIFRA, not a biocide under the EU Biocidal Products Regulation and not listed in 21 CFR 173.310; drinking-water rules regulate it through the aluminum it leaves behind and through NSF/ANSI/CAN 60 certification (status 2026-10-20).

It is not listed under EPA RMP or OSHA PSM, and 40 CFR 415 Subpart B covers alum producers, not plants that dose it. Coagulation beside disinfection is shown under drinking water treatment chemicals.

The table below compares the aluminum values and listings that apply to alum, with their type (status 2026-10-20).

How much aluminum may alum-treated drinking water contain?#

The 2 mg/L figure on NSF/ANSI/CAN 60 listings is a certification condition, not an EPA maximum contaminant level; the only federal aluminum value is the non-enforceable secondary standard of 0.05 to 0.2 mg/L (40 CFR 143.3). Health Canada sets a MAC of 2.9 mg/L with a 0.100 mg/L operational guidance value, and WHO gives a health-based value of 0.9 mg/L but no guideline value.

How Should Aluminum Sulfate Be Handled and Stored Safely?#

Liquid alum is an acidic solution (pH 1.5 to 2.8 for the iron-free grade, 0.2 to 1.0 for acidified grades) stored in rubber-lined, fiberglass, 316 stainless steel or plastic tanks, indoors or heated (ADWG; EPA supply chain profile, 2022).

Aluminum sulfate has no CLP Annex VI entry; the notified classification (ECHA C&L) is H318 (causes serious eye damage; Danger, GHS05) and H290 (may be corrosive to metals). NIOSH sets a REL of 2 mg/m³ TWA as Al (no OSHA PEL), and PPE and spill response follow the supplier SDS. Containment and sizing are covered under chemical storage tanks.

The table below summarizes aluminum sulfate storage and handling data.

What does an aluminum sulfate safety data sheet (SDS) cover?#

An aluminum sulfate safety data sheet gives the hazard classification, handling, storage, exposure-control and transport data for one specific product, and transport classification differs between liquid grades, so section 14 of the delivered grade decides.

Check the 4 items below against the delivered grade.

1. Confirm CAS 10043-01-3 and strength against the certificate of analysis.
2. Compare the hazard section with the notified H318 and H290.
3. Match the storage section to the tank material.
4. Read the transport entry in section 14.

What Are the Alternatives to Aluminum Sulfate?#

Five coagulants replace or supplement alum: polyaluminum chloride (PAC), aluminum chlorohydrate (ACH), sodium aluminate, ferric chloride and ferric sulfate, which differ mainly in alkalinity demand and in the residual metal they leave. Health Canada (2021) ranks alkalinity use from ACH (lowest) through PACl, then alum with ferric sulfate, to ferric chloride (highest).

The table below compares alum with its 5 alternatives.

Alum vs polyaluminum chloride (PAC)#

Polyaluminum chloride is prehydrolyzed to about 50 % basicity, so it consumes less alkalinity per mg of aluminum than alum at 0 % basicity. In cold water, one utility moves from alum to PAC below 12 °C (54 °F) and back above it. Basicity grades and doses are compared on polyaluminum chloride (PAC).

Alum vs aluminum chlorohydrate (ACH)#

Aluminum chlorohydrate carries 23 to 24 % Al2O3 at about 83 % basicity, against about 8.3 % Al2O3 and no basicity for liquid alum, and suppliers quote about one third of the liquid alum dose (WaterWorld, supplier-authored). The high-basicity product is covered under aluminum chlorohydrate (ACH).

Alum vs ferric chloride and ferric sulfate#

Ferric coagulants work over a wider pH range of 4 to 11 and leave iron instead of aluminum (US SMCL 0.3 mg/L); ferric chloride consumes 0.92 mg/L as CaCO3 per mg/L, against 0.50 for alum. By EPA's equivalence table, 10 mg/L of dry alum matches 5.5 mg/L of FeCl3. Strength and MUL are covered under ferric chloride, and the sulfate salt, with a 600 mg/L most common MUL, under ferric sulfate.

Aluminum Sulfate Grades, Suppliers and Sourcing#

Aluminum sulfate is sold in liquid (standard, iron-free, acidified) and dry (lump, granular, powder) grades, and EPA's 2022 supply chain profile names 7 producers. US production reached about 796 million kg in 2019, about 45 % of it consumed in the water sector, and EPA rated the supply-disruption risk Low.

The table lists the producers alphabetically; no company is a partner of this site and none pays for inclusion.

Buyers should check the NSF listing for the trade name and producing facility. Producers by region are listed under water treatment chemical suppliers.

How do buyers compare liquid alum offers?#

Liquid alum offers compare only on one basis: convert each quoted strength to cost per unit of dry alum or Al2O3 using the certificate of analysis; a wet ton of 48.5 % liquid holds about 0.485 dry tons of alum (calculated).

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 table below lists 4 dated bid ranges from municipal tabulations, each with its own basis.

The City of Concord, North Carolina, tabulation (bids opened 2024-06-04) shows USD 382.00 to 520.00 per dry ton of bulk liquid aluminum sulfate, while the City of Emporia, Virginia, tabulation (bids opened 2025-06-23) shows USD 117.86 to 244.00 per wet ton, two bases that differ by the 0.485 factor. A request states strength, the highest NSF/ANSI/CAN 60 dose as product and the documents: certificate of analysis, SDS, NSF certificate with MUL and an AWWA B403 statement. To send one specification to several sellers, request quotes for water treatment chemicals.

Where Does Alum Sit Among Coagulants for Water Treatment?#

Alum is the monomeric, 0 % basicity member of the inorganic aluminum and iron salts, one of 4 coagulant classes. All four classes are compared under coagulants for water treatment, and aluminum and iron salts side by side under inorganic coagulants.

Aluminum sulfate FAQs#

Is aluminum sulfate a coagulant or a flocculant?#

Aluminum sulfate is a coagulant: it neutralizes particle charge and forms aluminum hydroxide floc, while polymer flocculants then bridge particles into larger floc.

Polymer families are compared under flocculants for water treatment.

Does alum lower the pH of water?#

Yes: each mg/L of dry alum consumes 0.50 mg/L of alkalinity as CaCO3 and releases 0.44 mg/L of CO2, so pH falls in low-alkalinity water.

Lime, caustic and soda ash correct it, as covered under pH adjustment chemicals.

Does alum add sulfate to treated water?#

Yes: the sulfate in alum stays in solution, largely as calcium sulfate formed with bicarbonate hardness. The US secondary standard (40 CFR 143.3) and the EU indicator parameter both set sulfate at 250 mg/L.