Free Chlorine Test Results Guide

What this test measures

Free chlorine is the active sanitiser in your water — the part still available to kill bacteria. It’s the single most useful everyday check for pools and hot tubs, and it tells you how much treatment residual is reaching your tap.

The UK standard

There’s no fixed UK limit for chlorine in drinking water — suppliers keep a small, safe residual, typically around 0.5 mg/l or less at the tap. Pools are commonly maintained at roughly 1–3 mg/l free chlorine; follow your manufacturer’s guidance for hot tubs.

Reading your strip

Dip a strip into your sample for two seconds, hold it level and wait 30 seconds. Match the free chlorine pad against the colour chart on your instructions card and read off the closest band. Strips give you a clear range rather than a lab-precise number — exactly what you need for spotting problems and tracking changes over time.

What to do next

• Confirm it first. One strip is a snapshot — re-test with a fresh strip and a fresh sample before acting on a result.
• Low free chlorine in a pool or tub? Dose, circulate and re-test before anyone gets in.
• Zero chlorine at a tap on a mains supply is normal for some networks; a sudden strong chlorine taste that doesn’t settle is worth reporting to your supplier.
• Thinking about a filter? Test before and after fitting it so you can see exactly what it changed.