Worldwide, E. coli sampling is the standard way of showing that water is safe to drink.
E. coli is a good indicator of faecal contamination. If any E. coli is present, then this indicates that the source water is contaminated and treatment processes aren't coping, or there's a problem of some kind.
Other techniques suppliers use to check water quality include things like free available chlorine and turbidity (cloudiness) testing.
When a problem is found
When a problem is found, water suppliers must respond immediately. They need to find out where the contamination is and take steps to ensure water is safe. Large water suppliers, and many smaller suppliers, have a water safety plan documenting their planned response to events.
The supplier’s response may include:
- increased disinfection (like adding more chlorine to the water)
- taking steps to reduce exposure to the hazard (like by closing or changing a water source, or recommending that people boil all drinking-water)
- an enhanced sampling regime until they’re completely confident the water is safe.
These steps reduce the likelihood that anyone will get sick.
Issuing boil water notices
Suppliers may issue a boil water notice as part of a response. This isn’t a last resort – the community’s health is paramount and suppliers need to let them know there’s a problem with the water.
Boil water notices should remain in force until the water supply has returned to a satisfactory quality. They are temporary measure – they are not meant to be a permanent solution to a sub-standard supply.
Boil water notices may also be issued for other conditions, like if there’s an increase in the turbidity of tap water after heavy rain (which can indicate a breakdown in the treatment process), or when the water entering the distribution system is turbid and unchlorinated.