Water testing runs from a strip costing pennies to a laboratory panel costing a good deal more, and each step up answers questions the one below cannot. Matching the method to the question saves both money and the more expensive mistake of acting on a result the method could not actually support.
Strips
Cheap, instant and read by eye against a printed chart, which sets their limit. They are good for establishing a band, for repeat checks on a system you already understand, and for confirming something has changed. They are poor wherever a decision turns on a small difference, since color matching under kitchen lighting is imprecise, and they degrade with exposure to air, moisture and light in a way that makes them read wrong rather than obviously fail.
Reagent kits
Titration kits are the step up that matters for hardness, because the answer is a drop count rather than a color judgement, and the chemistry is specific to calcium and magnesium rather than responding to everything dissolved. Colorimetric kits for chlorine, iron and nitrate are similarly more precise than strips. They take a few minutes rather than seconds, cost more per test, and are the right choice whenever the figure is going to justify a purchase.
Meters
Conductivity and TDS pens are robust and instant and measure everything dissolved without distinguishing it, so their real job is tracking a reverse osmosis membrane's rejection rate over time rather than characterizing water. pH meters need two point calibration against fresh buffers and wet electrode storage to be trusted, and drift when neglected. Both are monitoring instruments for a system you understand, not diagnostic instruments for a supply you do not.
Laboratory analysis
The only method that answers whether the water is safe. Coliform bacteria, E. coli, nitrate, arsenic, lead and radon are all invisible to every device above, and clear water reading beautifully on a pen can carry any of them. The EPA notes private wells are not federally regulated under the Safe Drinking Water Act, so on a well the panel is the owner's to commission, annually at minimum. Our well water testing guide covers what a full panel should include.
Questions people ask about water testing devices
Are test strips good enough?
For establishing a band or checking a system you understand, yes. Not where a decision turns on a small difference.
What should I use for hardness?
A titration kit, since the result is a drop count and the chemistry is specific to calcium and magnesium.
What are TDS and pH meters actually for?
Monitoring a system you already understand, such as tracking a reverse osmosis membrane's rejection rate over time.
What needs a laboratory?
Anything about safety: coliform bacteria, E. coli, nitrate, arsenic, lead and radon are invisible to every home device.