Aqua ammonia for chloramination: the percentage is a basis question

Three forms, three different purchases

The 2022 Ten States Standards, §5.8.5, record that ammonia for chloramine formation “may be added to water either as a water solution of ammonium sulfate, or as aqua ammonia, or as anhydrous ammonia (purified 100% ammonia in liquid or gaseous form),” and then give separate design provisions for each. A solid dissolved on site, a solution delivered by tank truck and a liquefied gas under pressure are different purchases with different receiving equipment, and the choice between them is made in the design, before anyone writes a solicitation.

The same document discusses the chlorine-to-ammonia-nitrogen weight ratio as a design and operating matter. That ratio, any feed rate and any residual target belong to the engineer and the system’s operating plan; this guide reproduces no value and supplies no dose. The residual limit a public system must meet is a limit on the delivered water rather than a property of any chemical, a distinction set out in the water and wastewater treatment collection under “Which hypochlorite standard applies, and what you can read” and not repeated here.

Percent ammonia, percent ammonium hydroxide, weight or volume

The aggregated public record for ammonium hydroxide, CAS 1336-21-6, shows the basis problem in its own entries. One describes “a colorless aqueous solution. Concentration of ammonia ranges up to approximately 30%.” An HSDB entry says ammonia “is commonly encountered as aqueous solutions of 28 percent (aquammonia), called ammonium hydroxide and 10 percent, called household ammonia.” Another reads: “Strong ammonia soln (USP) is 27 to 30% (wt/vol) NH₃” — a weight-per-volume basis, in an undated secondary summary of a pharmacopeial monograph that was not read for this guide. A specific-gravity table at 20 °C/4 °C runs from 0.9939 at 1% to 0.8980 at 28% without restating what the percentages are percentages of.

The Ten States Standards add a fourth reading. Section 5.7.3 calls for “a bottle of concentrated ammonium hydroxide (56 per cent ammonia solution)” for chlorine leak detection. Read as percent NH₃, 56 does not sit with any of the figures above. Read as percent ammonium hydroxide by mass, it corresponds to about 27 percent NH₃, because the formula weights of NH₄OH and NH₃ are 35.05 and 17.03 — that conversion is this library’s arithmetic, and the document itself states no basis. When one design standard and one aggregated record can carry figures a factor of two apart for the same solution, a solicitation has to name the species, the mass or volume basis, the reference temperature and the method, and ask whether the figure is typical, a guaranteed limit or a measured lot result.

The shipping description is written in ammonia

The Hazardous Materials Table at 49 CFR 172.101 describes aqua ammonia by what is dissolved in it. “Ammonia solution, relative density between 0.880 and 0.957 at 15 degrees C in water, with more than 10 percent but not more than 35 percent ammonia” is hazard class 8, UN2672, packing group III. “Ammonia solution, relative density less than 0.880 at 15 degrees C in water, with more than 35 percent but not more than 50 percent ammonia” is Division 2.2, UN2073.

Both thresholds are written as percent ammonia with a relative density at 15 °C, so a figure quoted as percent ammonium hydroxide, or at another temperature, cannot be read against them without conversion. The shipping description on a particular delivery is the offeror’s determination and appears on its shipping papers and safety data sheet; this guide classifies nothing. The point for a buyer is narrower: the transport rule, like a careful specification, names its basis, and a solicitation that does not will be answered in whatever basis each bidder happens to use.

Listings carry bare percentages too

NSF’s search for certified drinking water treatment chemicals lists ammonium hydroxide as its own chemical name, separate from “Ammonia, Anhydrous” and “Ammonium Sulfate” — the three forms again, as three categories. On September 14, 2026 the ammonium hydroxide entries named product functions including Chloramination, pH Adjustment and Disinfection & Oxidation, each with a maximum use in mg/L, and trade designations ran from “Aqueous Ammonia - 5-15%” to “Aqueous Ammonia - 29.4%,” with “Aqua Ammonia 19%” and “Ammonium Hydroxide 19%” among them. Most state no basis at all.

So the certification record does not settle the basis question either; it identifies a product. Look up the entry by company, facility and trade designation, confirm the function the system uses, and write the concentration basis into the solicitation separately. The maximum use is a certification ceiling for that product and not a dose. AWWA’s catalogue lists B306-22, Aqua Ammonia (Liquid Ammonium Hydroxide), and B305-22, Anhydrous Ammonia, as its commodity standards; both are sold by AWWA and neither was read, so nothing here paraphrases them. Nothing in this library states that any Alliance product is certified or listed.

Vapour pressure belongs in the delivery specification

The International Chemical Safety Card entry on the aggregated record describes a “very volatile colourless ammonia solution in water with pungent odour,” and gives, for a 25% solution, a boiling point of 38 °C, a relative density of 0.9 and a vapour pressure of 48 kPa at 20 °C. An HSDB entry records that it “dissolves copper, zinc,” and that reaction with sulfuric acid or other strong mineral acids is exothermic. Those are the facts that shape a receiving arrangement, and they are why the Ten States Standards call, at §5.8.5, for closed, unpressurized, corrosion-resistant bulk and day tanks “vented through inert liquid traps to a high point outside,” for “an incompatible connector or lockout provisions” to prevent accidental addition of other chemicals to the bulk tank, and for storage designed so that temperature increases do not raise the ammonia vapour pressure above atmospheric.

A solicitation can match that installation: the dedicated connection the plant uses, the vent arrangement during unloading, the wetted materials the engineer has approved in light of the incompatibilities recorded above, the delivery temperature, and who is present when the load is transferred. Alliance sends a Certificate of Analysis when a customer asks, at no charge; name the assay, its basis and its method in the request, because a sample COA is not a lot certificate. Protective equipment and exposure controls are on the exact product’s safety data sheet. This is source-based editorial guidance, no original testing was performed for it, independent specialist review is pending, and nothing here states that any Alliance product is suitable, approved or recommended for chloramination or any other use.

• Which form of ammonia did the design select, and does the certification category match it?
• Is the concentration stated as percent NH₃ or percent ammonium hydroxide, by mass or by volume, at what temperature and by which method?
• What connection, vent arrangement and wetted materials does the receiving installation require?
• Who approved the chlorine-to-ammonia ratio and residual targets, as a design matter separate from this purchase?

Requirement → evidence → decision boundary

An editorial checklist for your review—not a table of product specifications.

Revision record

1.0 · September 14, 2026 — Source-based editorial edition. No original testing or product qualification is claimed.

For utilities, public works departments, public agencies and their procurement officers writing solicitations for treatment, fluoridation, chloramination and winter-maintenance chemistry. This collection does not interpret procurement law for any agency, determine the certification, qualification or eligibility of any product, set a dose, feed rate, chlorine-to-ammonia ratio, fluoride level or application rate, take a position on community water fluoridation, or make a compliance, permit, transport or waste determination.