Water supply system
Water purification facilities. After any solids in the water have settled out, the water is aerated. This is done by running it slowly over an aerated pebble bed, or through a sand bed. The oxygen in the water kills off the bacteria which are anaerobic. Sometimes poisonous red algae survive, and if so these are killed by adding chlorine to the water. The water is then examined (sampled) under a microscope, and its bacterial content recorded. There are standards set by government for the permitted limits to any kind of foreign objects and to the chemical and biological composition of the water.