Water · Water Testing
pH determines how effective your chlorine treatment actually is. A simple strip takes 5 seconds. Here is the number to aim for and why it matters more than most people realize.
The basics
When chlorine is added to water, it forms two species: hypochlorous acid (HOCl) and hypochlorite ion (OCl−). Hypochlorous acid is 70 to 80 times more effective as a disinfectant than hypochlorite ion. The ratio between the two depends entirely on pH. At pH 6, nearly all the chlorine exists as the more effective hypochlorous acid. At pH 8.5, the majority has shifted to the weaker hypochlorite form.
In practical terms: if you treat water at the correct bleach dose but the water pH is 8.5 or higher, your effective disinfection capacity is significantly reduced. The same dose of chlorine does less work. For most US tap water — which municipalities maintain between pH 7.0 and 7.5 — this is not a problem. For well water, collected rainwater, or water from unknown sources, pH can be outside this range.
The EPA drinking water secondary standard for pH is 6.5 to 8.5. For chlorine treatment to work well, aim for 6.5 to 7.5. Above 7.5 is acceptable but slightly less efficient; above 8.0 you should increase your chlorine dose or use a pH reducer before treating; above 8.5 standard chlorine dosing may not provide adequate disinfection.
For stored tap water filled from a treated municipal source and immediately sealed: pH testing is low priority — your tap water is already pH-controlled. For well water, collected rainwater, or any water from an untested source that you plan to treat with chlorine: check pH first. A strip read before you add bleach tells you whether to use a standard dose or a larger one.
Also useful at rotation time alongside chlorine residual strips. The two measurements together — residual chlorine still present and pH in range — give you confidence before drinking stored water.
A single pack of 50 to 100 strips covers years of testing. Keep them in the original capped tube with the desiccant packet, away from direct light and humidity. Most strips last 2 to 3 years before the reactive pads degrade. Pool pH strips, aquarium strips, or purpose-made drinking water pH strips all work for this purpose.
Where to buy
pH strips reading the 6 to 8.5 range are available at pool supply stores, pet stores (aquarium section), and Amazon. Any strip covering the 6–9 pH range in 0.5 increments is adequate. Packs of 100 are typically under $12.
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