Lancashire residents have been given advice by United Utilities over "musty" water today.
United Utilities said it had received reports of a slightly musty or earthy taste and odour to the drinking water in the Wigan, Chorley and South Ribble areas.
"This is due to an increase in the numbers of algae present in our lakes and reservoirs supplying these area," said a spokesman.
"Algae are normally present in reservoirs but this increase has been triggered by the recent hot weather conditions.
"While our treatment processes remove the algae themselves they produce a compound which causes this musty or earthy smell, even at extremely low concentrations.
"Some people are more sensitive to these compounds than others and can detect concentrations as low as a few nanograms per litre.
"These compounds are not harmful and we assure you that you can continue to use your water as normal."
The postcodes affected are WN1/WN5/WN6/PR6/PR7/L40