Water · Water Treatment
Measures dissolved minerals in your water. Useful for tracking filter performance, not for confirming safety. Know what it tells you and what it does not.
The basics
A TDS meter is a small handheld device that measures the total dissolved solids in water, reported in parts per million (ppm). Dissolved solids include minerals like calcium, magnesium, sodium, and potassium, along with trace amounts of other inorganic material. You dip the probe into a water sample, wait a few seconds, and read the number on the screen.
The most important thing to understand about a TDS meter is what it does not do. It does not detect bacteria, viruses, parasites, lead, pesticides, nitrates, or any specific contaminant. A TDS reading of zero does not mean water is safe to drink. A TDS reading of 300 does not necessarily mean water is unsafe. TDS is a measure of mineral content, not water quality in a safety sense.
Where a TDS meter earns its place is in monitoring filter performance. If your reverse osmosis system normally produces water at 10 ppm and you start seeing readings of 60 or 80, the membrane needs attention. If you are comparing a raw well water source against its filtered output, TDS gives you a fast, repeatable number. It is also a quick way to confirm whether a distiller is working properly, since distilled water should read near zero.
One meter per household is sufficient. They are compact, inexpensive, and last for years. Keep a spare battery (typically a coin cell) rather than a spare meter. Store it dry at room temperature. The electrode can foul over time with heavy use, but a rinse in clean water after each test extends the life significantly.
Brand does not matter. The HM Digital TDS-3 is a common and well-reviewed option, but any digital TDS pen in the $10 to $20 range will give you accurate-enough readings for household filter monitoring. Avoid units with features you do not need, like Bluetooth connectivity or app pairing. A simple probe and screen is all this job requires.
Where to buy
Search for "TDS meter" or "TDS pen" on Amazon or at your local hardware store. The HM Digital TDS-3 is a common choice, but any unit in the $10 to $20 range works for household use.
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