How to test water hardness at home
There are three ways to find out how hard your water is, and they answer slightly different questions. Your water company tells you about the supply zone. A test strip tells you about your tap. A titration kit tells you a number you can size equipment against.
1. Ask your water company — free, and the best starting point
Every UK water company publishes hardness for your postcode on their website. It is free, it takes a minute, and it is drawn from their own routine sampling, which is more testing than you will ever do yourself.
The limitation is that it describes a supply zone, not your kitchen. Zones get re-blended, properties sit near boundaries, and a building may have treatment already fitted that nobody mentioned when you moved in. It is the right first step and it is usually right — but it is not the same as testing your tap.
Use the postcode checker on this site to find out who supplies you and to go straight to their official page.
2. Test strips — cheap, quick, good enough for most decisions
A packet of hardness strips costs very little and gives you an answer in under a minute. You dip, you wait, you compare against a colour chart.
Strips give you a band rather than a precise number — soft, moderate, hard, very hard. For deciding whether you need a softener at all, a band is exactly what the decision turns on, so this is usually sufficient.
Two things spoil a strip test, and both are easy to avoid: reading it under artificial light, and using water that has stood in the pipe overnight. Run the tap first and read it by a window.
3. Titration kits — a real number
A titration kit gives you an actual figure. You measure a sample, add reagent drop by drop, and count the drops it takes to change colour. Each drop corresponds to a known increment of hardness.
Slower and slightly fiddly, but genuinely accurate, and it is what you want if you are sizing a softener, verifying that an installed softener is working, or checking whether that softener has run out of salt.
Check the reagent expiry date. Old reagents read low, which is the direction that leads to the wrong decision.
The kettle test, and why it is not enough
People often say they know their water is hard because the kettle furs up. That is a real signal and it is not wrong — but it tells you 'above about 200' and nothing more precise, and it takes weeks.
It is also not much use for the decision that actually costs money. Choosing between an inhibitor and a softener turns on where in the 150–300 range you sit, and a furred kettle cannot tell you that.
What to do with the answer
Under 150 mg/l CaCO₃: no scale problem. Any filtration you buy should be about taste, not hardness.
150–200: consider a scale inhibitor for the boiler. A softener is hard to justify.
200–250: genuinely open. Decide on what is bothering you rather than on the number.
Over 250: a softener is worth costing out properly, and scale protection on the boiler is close to essential.
Step by step
-
Run the tap
Run the cold kitchen tap for about thirty seconds. You want the water in the main, not water that has been sitting in the pipe overnight picking up character from it.
-
Fill a glass
Fill a clean glass with cold water. Do not use hot water — it has been through the cylinder or boiler and may already have dropped some of its hardness as scale.
-
Dip the strip
Dip the test strip in for the time stated on the packet, usually a second or two. Take it out and hold it level. Do not shake it.
-
Wait
Wait the stated development time, normally around fifteen to thirty seconds.
-
Compare
Compare the pads against the colour chart on the packet, in daylight rather than under a kitchen spotlight — artificial light shifts the colours and is the commonest source of a misread.
-
Record it
Write the figure and the date down. If you later fit a softener you will want the before number to check the after number against.