Water Knowledge

TDS

Summary: TDS (Total Dissolved Solids) is a measure of all dissolved minerals and salts in water—things like calcium, magnesium, sodium, chloride, sulfate, and bicarbonate. Higher TDS can affect taste and scale, but TDS does not identify specific contaminants. Use it as a quick trend check and pair it with lab tests when you need details.

Why homeowners should care

TDS influences taste (flat, salty, or mineral), scaling in heaters and appliances, and coffee/tea extraction. A TDS change can signal source mixing, seasonal road salt, or treatment performance (e.g., RO membranes). Because TDS is a summary number, it’s best for tracking trends—not for safety decisions by itself.

What TDS really measures

  • Units: mg/L or ppm (parts per million). Many “TDS pens” are actually conductivity meters that estimate TDS from EC using a conversion factor.
  • What’s inside TDS: Calcium, magnesium (hardness), sodium, potassium, chloride, sulfate, bicarbonate, silica, and more. Organic molecules contribute little to TDS.
  • Not a contaminant list: A high TDS doesn’t tell you which ions are high—run targeted lab tests to find the drivers (e.g., chloride, sulfate, sodium, hardness, alkalinity).

Where higher TDS can come from

  • Natural geology: Groundwater dissolving minerals from rock and soil.
  • Road salt or coastal influence: Seasonal increases in chloride/sodium raise TDS.
  • Blending/seasonal shifts: Utilities or multiple wells changing sources.
  • Treatment effects: Softening keeps TDS similar; reverse osmosis (RO) lowers TDS at the drinking tap.

When to test

  • Baseline a new home or private well.
  • Seasonally if you suspect salinity (road salt, drought, coastal intrusion).
  • Before/after installing or servicing RO to verify performance.
  • Any time taste becomes salty/flat or scale worsens.

How we test

HealthWaterLab can measure TDS in the lab and pair it with conductivity (EC), hardness, alkalinity, chloride, sulfate, and sodium to explain the number behind your TDS. For quick checks, many homeowners also use a handheld meter at the tap.

How to collect a good sample (or meter reading)

  • Use the kitchen cold-water tap (or the RO faucet if checking treated water).
  • Run water a minute or two to bring in fresh water (unless you’re intentionally measuring first-draw).
  • Rinse the TDS probe with sample water and avoid air bubbles on the sensors.
  • Note whether softening or RO is upstream; temperature affects readings slightly.

How to read your result

  • Lower TDS (e.g., RO water): Clean, neutral taste; good for coffee/tea and ice. Minerals may be too low for some taste preferences.
  • Moderate TDS: Typical of many groundwater sources; taste acceptable for most homes.
  • High TDS: Taste may be salty/flat; scale risk rises with hardness. Consider RO for drinking/cooking and manage scale in appliances.

Practical homeowner steps

  • Trend it: Log TDS by location and date; note weather/season and treatment status.
  • Find the drivers: If TDS rises, test chloride, sodium, sulfate, hardness, and alkalinity to see what’s changing.
  • Protect taste & gear: Use RO at the kitchen tap for high-TDS water; pair with a softener to reduce scale house-wide.
  • Dial in flavor: If RO tastes too “flat,” add a small remineralization cartridge for coffee/tea balance.

FAQ

Does high TDS mean my water is unsafe?

Not by itself. TDS is an indicator of total ions, not a safety test. Run targeted lab tests (e.g., chloride, sodium, sulfate, nitrate) if TDS changes or taste is off.

Why didn’t my softener lower TDS?

Softeners exchange calcium/magnesium for sodium or potassium. Total ions stay similar, so TDS changes little. RO is what lowers TDS at a drinking tap.

What TDS is “good” for drinking?

Preference varies. Many people like 50–300 ppm for taste. Very low TDS (RO) tastes clean but can seem “flat”; very high TDS can taste salty or mineral.

Is a TDS meter accurate?

It’s accurate for trends, but it estimates ppm from conductivity and doesn’t identify specific ions. Use lab tests to diagnose what’s behind the number.

Why did TDS jump in winter?

Road salt runoff can raise chloride/sodium in shallow aquifers or distribution mains. Track TDS with chloride/sodium tests to confirm.

My RO TDS is creeping up—what does that mean?

RO membranes and prefilters may be due for service. A slow rise at the RO faucet is a common maintenance cue—replace filters and retest.

Will carbon filters reduce TDS?

No. Carbon improves taste/odor (e.g., chlorine) but doesn’t remove dissolved ions. RO or distillation reduces TDS; softeners address scale, not TDS.

Does TDS affect coffee, tea, and ice?

Yes. TDS influences extraction and mouthfeel. Many coffee makers prefer moderate TDS; RO plus a small remineralization cartridge gives consistent results.

Is high TDS bad for aquariums or humidifiers?

It can cause scale and stress some species. Many aquarium owners use RO/DI and remineralize to target chemistry. Use RO for humidifiers to reduce white dust.

Do I need to lower TDS for health?

Not necessarily. TDS reflects minerals, many of which are benign. If taste or scale is a problem—or chloride/sodium are high—use RO at the drinking tap and manage hardness house-wide.

Want to make sense of your TDS? See kits and step-by-step guidance at HealthWaterLab.com.