Thousands of people living in Clevedon will have to boil their water until at least Monday after the supply was found to be contaminated.
Bristol Water says it detected the parasite cryptosporidium which can cause vomiting and diarrhoea.
Two of the town's schools had to be closed as a result, and bottled water has been handed out to residents and care homes.
Bristol Water has confirmed this morning (January 13) that a number of properties in Clevedon are still advised to boil all water before consuming it this weekend.
Posting on social media, the water company reminded residents that had received a warning postcard, had to take extra care before consuming water.
Bristol Water is aiming to be in a position to confirm the boil notice removal on Monday morning, before customers start their morning routines.
This is subject to the results of the Sunday afternoon sample and PHE approval.