TDS in one paragraph
Total dissolved solids is the combined weight of everything dissolved in your water — mostly harmless minerals like calcium, magnesium, sodium, and bicarbonates, measured in milligrams per liter (same as parts per million). A pocket TDS meter doesn't even count those directly: it measures electrical conductivity and estimates the total. It cannot tell calcium from sodium, let alone detect lead, bacteria, or PFAS. It reports how much is dissolved, with no idea what.
What high and low readings actually mean
- High TDS (say, 300–500+) — usually just mineral-rich water. In limestone country like the Lehigh Valley, hardness minerals push TDS up harmlessly. Taste can turn flat or salty at the top end, and unusually high readings are a reason to find out which solids — but the number itself is not a hazard.
- Low TDS (under ~50) — mineral-light water, typical of Pocono wells and mountain-reservoir city supplies. Often tastes crisp. Not a safety certificate: water can read 20 on the meter and still carry lead from old solder or coliform bacteria, neither of which registers.
- The 500 mg/L "limit" — an EPA secondary standard, meaning aesthetic guidance about taste and scaling, not a health rule. Plenty of safe supplies run above it; plenty of unsafe water runs far below it.
The two sales demos to walk away from
Demo one: the TDS meter as a safety test. A salesperson dips a meter in your tap water, shows a three-digit number, and lets alarm do the selling. Now you know better: the number is mostly calcium and friends. Ask what the solids are — the honest follow-up the demo is designed to skip.
Demo two: the "precipitator." Two electrodes go into a glass of your water, current flows, and the water turns a horrifying brown. The brown is iron oxide from the device's own corroding electrode — electrolysis theater that performs identically in nearly any mineral-containing water, including expensive bottled brands. It demonstrates that your water conducts electricity, which mineral water does. That's all.
Our commitment runs the other way: measurements explained in plain English, including the ones that come back boring. Boring results are good news, and we deliver them as such.
Where TDS genuinely earns its place
On our tests and service visits, TDS is the reverse osmosis scoreboard. An RO membrane strips most dissolved solids, so comparing the tap reading to the RO-faucet reading shows the system working — typically a 90%+ drop — and a creeping output number flags an aging membrane before your taste buds notice. That's a legitimate, useful job for a twelve-dollar meter: performance monitoring, not fear marketing.
It's also honest context: if you're choosing between a pitcher and reverse osmosis, note that carbon pitchers barely move TDS at all — carbon grabs chlorine and organics, not dissolved minerals. Only RO (or distillation) meaningfully lowers the number. Whether you need it lowered is a taste-and-chemistry conversation, and the free test is where it starts.