You are in site section: Online features

About water quality

About water quality

Explanation of terms

A colour photo of Sandy Dellwo from the Murray Catchment Management Authority.
Sandy Dellwo. Photo: Lyn Kennedy.

Turbidity

Turbidity is the cloudiness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air.

The measurement of turbidity is a key test of water quality.

Turbidity measured this way uses an instrument called a nephelometer with the detector setup to the side of the light beam. Less light reaches the detector if there are lots of small particles scattering the source beam than if there are few.

The units of turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU).
(Source: Wikipedia)


pH

pH is an expression for the effective concentration of hydrogen ions in solution. It is a logrythmic scale with 7 indicating neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

mg/L

This is an indication of the concentration of any substance in terms of milligrams per litre.

µS/cm

Salty water conducts electricity more effectively than fresh water. An electrical conductivity meter monitors the strength of a small current moving through water from one probe to the other. This is measured in µS/cm. This is the conductance as measured between the opposite faces of a 1-cm cube of material. This measurement has units of Siemens/cm. In water testing the units are in microsiemens/cm (µS/cm.)

ppm

Parts per million: a unit of measurement noting the amount of dissolved solids in a solution in terms of a ratio between the number of parts of solids to a million parts of total volume. The substance doesn't matter, phosphates or dissolved oxygen.

Assessment and standards

Aimee Link, North Rhine River, South Australia.
Aimee Link, North Rhine River, South Australia.

Water quality is assessed in terms of its purposed use and source. Our expectations of municipal drinking water are far different than water we would find acceptable for irrigating crops or watering stock. Waterwatch generally looks at water quality in terms of its ability to support aquatic life. We use this standard, as water that supports a high quality aquatic habitat also will support all human uses as well.

Where water comes from is also a factor in the sort of quality we can expect. Mountain streams bubbling down a hillside are expected to be much cleaner than a lowland river or an urban pond. Waterwatch defines ideas concerning a waterway's quality based on what we would expect of it under ideal conditions that have a positive impact on any fresh water body.

These include:

  • Well vegetated riparian area (50-100 meters around a body of water)
  • Stable banks
  • Minimal disturbance by non-native animals
  • Minimal non-point and point source pollution

If the above terms are met Waterwatch would expect the following:

Up-land streams, rivers

Turbidity <10NTU
pH 6.5 to 9
Nitrates nil
Salinity <800µS
Phosphates nil
Dissolved Oxygen >6mg/L

Low Land Rivers

Turbidity <30NTU
pH 6 to 9
Nitrates <30mg/L
Salinity <800µS
Phosphates <0.05mg/L
Dissolved Oxygen >4mg/L

Ponds, Dams, Billabongs

Turbidity <30NTU
pH 6 to 9
Nitrates <30mg/L
Salinity <800µS
Phosphates <0.05mg/L
Dissolved Oxygen >4mg/L

Local geology and biology can also sometimes play a factor. For instance, in North American deciduous forests, leaves falling into the water create carbonic acid, and so a pH as low as 4 can be normal. Conversely, here in the ACT, the limestone outcrops significantly raise the expected pH.