Bromate, UV & Disinfection Byproducts in Open Water

Open finished-water and source-water reservoirs face a subtle chemistry problem: sunlight can create regulated contaminants. The best-known example is bromate.

How bromate forms

Bromate (BrO₃⁻) can form when water that contains bromide and a chlorine-based disinfectant is exposed to sunlight (UV). The photochemical pathway converts otherwise-acceptable constituents into bromate, which drinking-water regulations limit because of health concerns. Utilities that would never have a bromate problem in the dark can develop one simply because their water sits in the sun.

Why blocking light helps

Because the reaction is driven by sunlight, removing the light removes much of the driver. A dense floating cover that blocks UV at the surface:

• Cuts the photochemical formation of bromate by shading the water.
• Suppresses algae and cyanobacteria, which also depend on light and can themselves create taste, odor, and treatment problems.
• Does this without adding chemicals — a passive, physical control.

This UV-blocking benefit, alongside evaporation reduction, is a major reason hollow-ball covers were first adopted on drinking-water reservoirs.

What this means for an operator

If you manage an open reservoir where bromide is present and chlorine-based disinfection is used, sunlight is a variable worth controlling. A floating ball cover is one of the simplest ways to do it: it pours on, needs no anchoring, lets rain and snow pass, and can be pushed aside for equipment access.

Material note: Armor Ball® is molded from UV-stabilized HDPE specified for potable-water/food-contact use when required. Material certifications, SDS, and NSF/ANSI 61 documentation where applicable are available on request.

Learn more: Is HDPE safe for potable water? · Algae control · Reservoirs & water storage