Carbonate Water Test Results Guide

What this test measures

Carbonate measures the dissolved carbonate minerals in your water — the chemistry behind kettle furring and the white crust on taps. It’s closely linked to alkalinity, and in aquariums it’s the KH reading that keeps water stable for fish.

The UK standard

There is no legal limit for carbonate in UK drinking water — it’s a natural mineral measure, not a contaminant. What matters is what it does: higher carbonate water leaves more scale on heating elements and glass.

Reading your strip

Dip a strip into your sample for two seconds, hold it level and wait 30 seconds. Match the carbonate 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.
• High carbonate plus high hardness means limescale — descale kettles regularly and consider scale protection for boilers and showers.
• Aquarium owners: sudden drops in carbonate (KH) can let pH swing dangerously — re-test after water changes.
• Thinking about a filter? Test before and after fitting it so you can see exactly what it changed.