Nitrite Water Test Results Guide

What this test measures

This test measures nitrite. In drinking water it can point to contamination or treatment issues; in aquariums it’s a critical reading, because even small amounts of nitrite are harmful to fish.

The UK standard

The UK drinking water standard is 0.5 mg/l for nitrite at the tap. In a mature aquarium the target is effectively zero — any measurable nitrite means the filter cycle needs attention.

Reading your strip

Dip a strip into your sample for two seconds, hold it level and wait 30 seconds. Match the nitrite 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.
• Aquarium reading above zero? Partial water change, check the filter, feed lightly and re-test daily until it settles.
• If a reading on a mains supply stays above the standard after re-testing, contact your water supplier — they investigate quality concerns free of charge.
• On a private supply (well, borehole or spring), your local council’s environmental health team can arrange accredited lab testing.
• Thinking about a filter? Test before and after fitting it so you can see exactly what it changed.