To check the pH level of water you need a reagent or an electrode plus a sample that has not had time to change, and the second part is where most home tests go wrong. Water straight from the tap is in equilibrium with the pressure and dissolved gases in the pipe, and once it sits in an open cup the carbon dioxide starts leaving and the reading rises. Test fresh, test cold, and use the same method every time so results are comparable.
The three ways to measure it
Test strips are the quickest: dip, wait the printed time, and match the pad against the color chart in daylight. They are coarse but fine for spotting an obviously acidic or alkaline supply. A liquid drop kit adds a reagent to a measured sample and reads the resulting color against a comparator, which is a step more precise and much less sensitive to a damp storage cupboard. A digital pen meter gives a numeric reading and is the only method that resolves small changes, but it is only as good as its last calibration, and an uncalibrated pen is confidently wrong rather than approximately right. For anything you plan to spend money on, send a sample to a laboratory.
Taking a sample that tells the truth
Run the cold tap for a good while first, so you are testing the supply rather than water that sat in the plumbing overnight and picked up metals and gases from it. Fill a clean container to the brim and test immediately. Do not test water that has been standing, stirred, aerated or carried around in a sports bottle, because all of those shift the result upward. Temperature matters as well, since electrodes read differently in cold and warm water, which is why decent meters carry automatic temperature compensation. On a well, take one sample as close to the wellhead as you can and one at a treated tap, because the difference between them is what tells you whether your own equipment is moving the pH.
Calibrating and caring for a meter
A pH pen is calibrated against buffer solutions of known value, normally two of them bracketing the range you expect, and it needs recalibrating regularly rather than once when it arrives. Buffers expire, so replace them rather than topping up an old bottle. The electrode must be stored wet in the manufacturer's storage solution: storing it dry, or in distilled water, damages the sensing glass and produces readings that drift slowly enough that you may not notice. Rinse between samples with a little of the next sample rather than wiping the tip, which builds a static charge and unsettles the reading.
What the reading tells you to do
Acidic water is corrosive, and the evidence usually appears before the test does: blue-green staining in sinks and tubs from dissolved copper, pinhole leaks in copper lines, and a metallic taste. The usual fix is an acid neutralizer tank ahead of the rest of the treatment train. Alkaline water is less damaging but drives scale and can make water taste soda-like. pH also decides what other equipment can do: Penn State Extension notes that a softener will only remove dissolved iron when pH is above 6.7, hardness is between 3 and 20 grains per gallon and dissolved iron is under 5 mg/L, so a low pH result can be the reason an iron problem is not responding. Our guide to the best TDS level for drinking water covers the companion measurement.
Questions people ask about how to check ph level of water
What is the quickest way to check the pH of tap water?
A test strip dipped in a freshly drawn cup of cold water and read at the time printed on the bottle. It is coarse, but it will tell you immediately whether the supply is clearly acidic or clearly alkaline.
Why does my reading change if I test the same water twice?
Usually because the sample has been sitting. Dissolved carbon dioxide escapes from standing water and pushes the reading up, so test immediately after drawing and do not reuse a sample.
Do I need to calibrate a pH meter?
Yes, with fresh buffer solutions and on a regular schedule. An uncalibrated meter still displays a confident number, which is more misleading than a strip that at least looks approximate.
Should I check pH at the wellhead or at the tap?
Both. The wellhead sample is your raw water, the tap sample is what your treatment equipment is producing, and the difference between the two is the only way to see what the equipment is doing.