Windblown ash from the massive mountain fire still burning above Gordon's Bay has affected the taste of Cape Town's water, the city said on Wednesday.

However the "different, antiseptic" taste posed no health threat, the water and sanitation department said in a statement.

It said it had been getting calls from concerned residents following the fire, which has been burning in the catchment area of the Steenbras dam, one of Cape Town's major water sources.

It said the taste of the ash became noticeable in concentrations as low as one millionth of a gram per litre, and was not being completely removed by the water treatment process.

The taste should return to normal in the next two weeks.

Sapa