Water testing can feel a bit like detective work. Three common clues investigators chase are conductivity, salinity, and TDS. They’re related, they often travel together, but they’re not the same thing. Here’s a quick, news-style explainer that clears up the confusion. Using a single HORIBA meter (distributed in Australia by Australian Scientific) allows for these measurements in the field.
What is Conductivity
Conductivity measures how well water carries an electrical current. That happens because dissolved ions (like sodium, chloride, sulfate) act as tiny charge carriers. So when your meter reads µS/cm or mS/cm, it’s telling you how many “ion highways” are in the sample — a direct physical measurement, not a guess. Good meters (like the LAQUA series) include temperature compensation and multi-point calibration to keep that number accurate across environments.
What is TDS (Total Dissolved Solids)
TDS (Total Dissolved Solids) reports the mass of dissolved substances — usually in mg/L or ppm. But handheld meters don’t weigh solids; they estimate TDS from conductivity using a conversion factor. That factor depends on the types of ions in the water (NaCl behaves differently to calcium bicarbonate). So TDS from a conductivity reading is an approximation unless you’ve matched the factor to your sample. HORIBA meters offer selectable TDS curves (EN27888, 442, NaCl, etc.) to improve that estimate.
What is Salinity?
Salinity specifically expresses the concentration of dissolved salts (commonly in ppt or PSU). Like TDS, salinity is usually derived from conductivity. The conversion depends on the salt mix (open ocean seawater vs. brackish river water). HORIBA devices include salinity-calibration options (NaCl or seawater curves) so the meter can give a more meaningful “saltiness” number for your application.
How Conductivity, TDS, and Salinity are Related
A modern LAQUA handheld will show conductivity, then convert and display TDS and salinity using built-in curves and auto temperature compensation — handy when you need fast answers on site. But remember: the primary measurement is conductivity. TDS and salinity are useful derived values — great for trends and quick decisions, but if you need absolute accuracy ,confirm with lab analysis or choose the correct conversion curve and calibrate often.
Bottom line:
Think of conductivity as the hard data, and TDS/salinity as the helpful translations. Use a quality meter (like our HORIBA’s LAQUA Range), keep it calibrated, pick the right conversion curves, and you’ll get field numbers that actually mean something.