The five parameters at a glance

pH - acidity and alkalinity

pH measures how acidic or alkaline water is, on a scale from 0 to 14. Below 7 is acidic, above 7 is alkaline, and 7 is neutral.

The scale is logarithmic, so each whole number is a tenfold change. Water at pH 6 is ten times more acidic than water at pH 7, not slightly more.

Why it matters: even small pH shifts can harm aquatic life, corrode pipes and equipment, or throw off chemical dosing.

EC - electrical conductivity

EC measures how well water conducts electricity, which depends on the amount of dissolved salts and minerals in it. Pure water is a poor conductor - the more dissolved ions, the higher the reading.

Why it matters: it's a fast way to track salinity and pollution, and to check whether water is suitable for irrigation or process use. A sudden change in EC is often the first sign that something has entered a water body that shouldn't be there.

EC readings change with temperature, so they're normally compensated to 25 °C to make them comparable. Most meters handle this automatically.

DO - dissolved oxygen

DO measures how much oxygen is dissolved in water - the same oxygen aquatic life breathes. It's reported either as a concentration (mg/L) or as a percentage of what the water could hold at that temperature and pressure (% saturation).

Why it matters: low DO stresses or kills fish and other organisms, and often signals pollution or poor circulation.

DO is also the most time-sensitive parameter on this list. Oxygen levels swing through the day as aquatic plants photosynthesise and respire, so when you sample matters as much as where.

ORP - oxidation-reduction potential

ORP measures water's tendency to oxidise or reduce other substances. In plain terms: how strongly it can clean or break things down. It's reported in millivolts, and can be positive or negative.

Why it matters: it's a quick check on disinfection strength in treated water, and on corrosion risk in industrial systems.

ORP is a measure of oxidising strength rather than of any particular chemical, so it tells you how effectively water can disinfect without telling you what's doing the disinfecting.

NTU - turbidity

NTU measures turbidity, or how cloudy water is, caused by suspended particles like silt, algae or sediment. The unit stands for Nephelometric Turbidity Units, which describes the method: shining light through a sample and measuring how much of it scatters.

Why it matters: cloudy water can mean poor filtration, sediment runoff, or unsafe drinking water. Suspended particles also shelter microorganisms from disinfection, so high turbidity undermines treatment that would otherwise work.

This is the one parameter here you can sometimes judge by eye - but only roughly, and only at the higher end. Water that looks perfectly clear can still carry enough suspended material to matter.

Why measuring all five matters

Each parameter answers a different question, and any one of them on its own can be misleading. Low DO tells you there's a problem; EC and turbidity often tell you where it came from.

• They catch problems you can't see. Four of the five give away nothing visually.
• They confirm treatment and filtration are working rather than assuming they are.
• They protect rivers, lakes and groundwater by catching changes early enough to act on.
• They support water that's fit for its purpose. Irrigation, process use, drinking water and aquaculture all have different requirements.

The parameters also interact. Temperature affects both DO saturation and EC readings. Turbidity can interfere with optical measurements. Reading them together gives you a picture that no single parameter can.

Common questions