More than 270 schools in Lancashire have been urged to check their water status with the new term approaching.
Even though some are in areas where the boil water alert has now been lifted, it is thought many could still be under restrictions when the first pupils return.
United Utilities, who declared an all-clear for 80,000 households and businesses on Thursday night, are still working to clean up supplies to the remaining 220,000 affected.
The company expects to have lifted the alert in most parts of Preston, South Ribble, Chorley and the Fylde Coast by the end of next week, although a small minority of neighbourhoods could still have restrictions going on into the following week.
Officials say they have been trying to contact all 277 schools in the affected area but, because of the summer holidays, they have only managed to speak to about half.
“We hope to be able to lift the boil water advice in the coming week,” said a spokesman. “But this means some schools may return with the advice still in place.
“We want to ensure that all schools and other educational establishments in the affected area are supplied with clean drinking water to support term opening by deploying bottled water.
“Working with the local authorities, we have called the 277 schools in the affected area but have yet to speak directly with around half of them.
“If you haven’t spoken with us yet, can you please contact us directly to discuss your particular needs – we have already made 70 appointments to deliver bottled water following agreement with schools.
“You can email us via School.ContactLine@uuplc.co.uk or call us on 0800 912 7240.”