West Auckland residents complaining of "earthy" tasting water are being offered free bottles of water and told the problem might not be fixed until tomorrow.
Watercare began receiving complaints yesterday from residents who are served by the Titirangi reservoirs. Laingholm, Blockhouse Bay and Te Atatu are amongst the affected areas.
The odd taste has been caused by hot weather stimulating algal bloom in a water storage dam in the Waitakere Ranges. Despite having tests in place the problem was not detected by the treatment plant's sensory panel until the complaints came in. Usually, it is detected and the water put through a carbon dosing process.
Operations manager Shayne Cunis said the water was now being put through a carbon dosing process. It continued to meet the national drinking water standards and posed no health risk.
Testing this morning at some households showed the measures were working.
However, Mr Cunis said some customers may experience the problem for a further 24 hours and bottled water was available on request.
Algal bloom in the storage lakes to the west of the city is not without precedent. In 2000, Waitakere lakes had four months off mains supply because of bloom affecting taste.