Your landlord can interrupt utility service for a "brief" period in order to allow repairs, but should give you advance notice so you can plan accordingly. However, if you have not formally objected to being without water you should do so promptly, in writing, so your landlord knows that you object. This may spark a discussion with your landlord about the basis for the lack of water during the day.
If it continues without reasonable excuse, take a copy of your objection letter to the City/County Building department and ask for an inspection. The City or County may have no idea this is happening.
Water is a fundemental component of a tenancy. Having maintenance performed is also important, but the landlord has a duty to keep the place to code, and codes always require continuous clean water.
Hope this helps. Elizabeth Powell