Portsmouth Water said the sample was taken from a fire hydrant in Martin Close in Lee-on-the-Solent during routine testing.

Residents in Martin Close, Bullfinch Court, Magpie Lane and Chaffinch Way have now been told to boil water before drinking or using it for cooking, brushing teeth and hand-washing dishes.

This includes properties with boiling water taps, filters or softeners.

The company said further tests are under way and bottled water is being delivered. Supplies are not affected elsewhere.