Before you buy or adjust a softener, you need a hardness number. You can get one yourself with a home test kit, or you can send a water sample to a lab. Both are reasonable. The right choice depends on what the number is for, how much you need to trust it, and who will read it. A quick check to see whether hardness is worth investigating needs different accuracy than a number that a provider will use to set the regeneration schedule.
Decide what the number is for
Name the decision first. If you are only checking whether hard water is likely, a home test is enough to tell you whether to keep going. If you are comparing softener quotes, setting a control, or responding to a warranty question, get a lab result with a clear report, because the number will be used to make a commitment.
What a home test gives you
Home test kits are quick and can be run in the kitchen. Follow the instructions exactly, since timing, temperature and the number of drops or strips change the result. Compare the color against the chart in good light, and record the result with the date you tested. Expect the reading to be approximate. A home test is a screening tool, and it may not separate hardness from other dissolved minerals that show up in some water.
What a lab report gives you
A lab report states the result with units, the method used, and often the detection limits. Check that the report lists the units, since hardness can be stated in more than one unit, and that the number you compare against uses the same unit. Ask whether the lab tests for other conditions that could affect a softener choice, and whether the report includes a note on the sample condition.
Take the sample the right way
Where you draw the sample changes the result. For a softener decision, test the water before it reaches the softener, usually at a cold tap close to where the line enters the house, and test again after the softener, at a tap that uses softened water. Run the cold tap for a short time before filling the bottle if the water has been sitting in the pipes, and note in writing if you did not. Use the bottle the lab supplies, follow its instructions on storage, and ship or drop it off within the time the lab allows.
Compare the two results
If the home test and the lab report disagree, do not pick the one you like. Ask why. Often the difference comes from the test method, the timing, or the sample location. A provider who sizes a unit should use the same number you have on record, so give every provider the same report. The buyer's guide covers how to put the water data in front of providers, and our methodology page explains why we ask every provider to size against the same input.