Running water

A catchment is just what it sounds like: an area of land that catches rain water as it falls from the sky, then runs off trees and the surrounding land. Gravity makes water flow along a one-way path from high to low land, through the catchment and into a creek or river, and sometimes into a reservoir.

We collect water by building dams. This has been going on for thousands of years -- the world's oldest dam on the Nile River in Egypt was built 4 700 years ago. But water brings to the dam any wastes, nutrients, poisons, germs and other pollutants it has collected along the way. The best way to protect water quality at the dam is to protect the source of the water -- in other words, the catchment. It's hard to reverse the damage once it's done, so it's better to have clean water flowing through a healthy environment than to disinfect polluted water.

Many of us remember Sydney's water quality scare in 1998, when the micro-organisms Cryptosporidium and Giardia were detected in drinking water. People boiled water or bought bottled water for a couple of months until the water was healthy again. Although nobody became sick from the micro-organisms, the situation showed that catchments collecting water for a large population need to be carefully managed. An inquiry into the incident found that a new authority was needed to reduce the possibility of contamination happening again. So the Sydney Catchment Authority (SCA) was formed in July 1999.

The SCA looks after all of Sydney's water supply catchments, dams and reservoirs, as well as the pipes, tunnels, canals and pumps delivering over 1600 megalitres of water to Sydney Water. Sydney Water then treats the water before distributing it to the people of Sydney, Wollongong and surrounding areas. Sydney's water quality is already high, but filtering makes it even cleaner. Screens pass nothing wider than half a hair's width, removing twigs, weeds and fish. A flocculant is then added, causing remaining impurities to clump together. Water is then refiltered and disinfected using chlorine. Fluoride is added to protect your teeth.

The water is constantly tested in the catchment area, dams and filtration plants to ensure purity. In addition to routine monitoring for blue-green algae and pollutants, daily tests for Cryptosporidium and Giardia are performed at selected sites in the catchment, especially those near sewage treatment plants.