Health risks

The greatest risk comes from microbial contamination.  The main source of microbes such as bacteria and viruses is from the drinking water contaminated with faeces from humans or animals (including birds).  Other microbial hazards include Legionella, a bacteria that can grow in water systems, and toxic blue-green algae (more correctly called cyanobacteria) that can grow in lakes and reservoirs. 

Chemicals can also affect water quality.  Sources of chemicals in water include:

• chemicals from industrial or agricultural activities such as pesticides and heating oil
• naturally occurring chemicals such as rocks rich in metals such as arsenic and iron
• chemicals from the water treatment process
• from materials that come into contact with water such as pipes made from lead

The main radiological hazard is radon, a naturally occurring radioactive gas, that can sometimes be found in drinking water.

Water companies have water safety plans to manage the risks from microbes, chemicals and radiological hazards in drinking water and to ensure that they meet health-based standards.  These plans include drinking water treatment processes including disinfection and filters to remove contaminants and quality control such as monitoring water quality at source and at the consumers tap.