Water quality issues

As part of its water quality monitoring duties, the Sydney Catchment Authority (SCA) works to ensure that water in the catchments and entering the storages, meets or exceeds agreed standards.

Of particular concern are algae, microorganisms and bacteria, as well as the nutrients that promote their growth. This phenomenon is called eutrophication.

Heavy metals from current and disused mining sites are also monitored.

The SCA produces an annual water quality monitoring report documenting in detail the quality and composition of water at dozens of measuring points around the catchments. It also compares the last 10 years of data at the different monitoring sites.

Concentrations of metal (eg iron) and elements (eg manganese), as well as nutrients (eg nitrogen), are presented in detailed graphs.

The 1998 water incident highlighted the existence of the protozoa (single cell animals) Cryptosporidium and Giardia in some parts of the catchments. Vigorous measures are now in place to monitor protozoa and the SCA, in tandem with independent laboratories, closely monitors potential 'hotspots'.

Water quality in reservoirs

Water quality in reservoirs can vary considerably, depending on numerous factors.

Within reservoirs, water quality varies at different depths and temperatures, and further varies depending on the time of year.

In summer, a warm upper layer (epilimnion) develops above a considerably colder lower layer (hypolimnion). A much narrower layer, known as a thermocline, separates the two strata.

The hypolimnion can become depleted in oxygen (anoxic), while the warmer epilimnion is in danger of encouraging nutrient concentrations and algal growth.

Dam managers use a process known as artificial destratification to mix the layers. Air is pumped into the lake near the bottom, forming a 'plume'. This must be done carefully because if destratification is performed at the wrong time water quality could decrease.

A chain of thermal resistors (thermistors) suspended in the lake closely monitors water temperature, and hence quality. The data enables managers to determine from where to draw the best quality water for customer supply.