On a municipal supply, testing your own tap water is not the same proposition as testing a well, because a great deal of testing has already been done and published. The useful question is what a home kit tells you that the utility's report does not, and the answer is specific: everything that happens between the water main and your tap.
Read the report first, it is free
The EPA requires every community water system to publish an annual Consumer Confidence Report and maintains a finder for them. It covers the regulated contaminants, the disinfectant used, hardness in many cases, and any violations during the year, all measured to laboratory standard on a monitoring schedule no home kit approaches. Anything the report already answers does not need buying a kit for. Start there, and use it to decide what remains genuinely unknown about the water arriving at your own fixtures.
What the report cannot tell you
It describes water leaving the plant and sampled around the distribution system, not water leaving your tap. Lead is the clearest example, since it typically enters from a lead service line, from lead solder in older properties or from brass fittings, all of which are on your side of the meter. Copper from corroding pipework is the same. So is anything contributed by an old water heater, a long dead leg, or a filter that has been left in place far too long. Those are exactly what a home test addresses.
Which tests are worth doing at home
Hardness, using a titration kit or strips, since the figure decides whether a softener pays and how it is set. Chlorine, to see what is arriving and to check a filter is working. A first draw lead test, which is the most valuable single test in an older property and is best sent to a laboratory rather than read from a strip. pH is quick and useful. Skip broad multi parameter strip packs promising dozens of results: they are imprecise and encourage conclusions the chemistry does not support.
Sampling so the result means something
Match the sample to the question. For lead, take a first draw after water has stood in the pipes for several hours, since that is what shows contribution from the plumbing, and a flushed sample afterwards to separate the service line from the fixture. For everything else, run until cold and steady with the aerator removed, so you are measuring the supply. Test at the same tap each time so results are comparable. Our water testing guide covers when to escalate to a laboratory.
Questions people ask about tap water testing kit
Do I need to test if my utility publishes a report?
For the regulated contaminants, no. A home test answers what happens between the water main and your own tap, which the report cannot cover.
What is the most useful test in an older home?
A first draw lead test after water has stood several hours, sent to a laboratory rather than read from a strip.
Are multi parameter test strips worth buying?
Rarely. Broad strip packs are imprecise and encourage conclusions the chemistry does not support. Single purpose kits are far more reliable.
How should I take a general sample?
From a cold tap with the aerator removed, after running until the water is cold and steady, at the same tap each time.