The simple answer is – very frequently! Cats love fresh and cool water and ideally would prefer to have a source of running water. Cat water bowls need to be thoroughly cleaned every 24 hours but will need to be topped up several times a day.
As soon as the water bowl gets contaminated with dust, dirt or food, you will need to clean it and fill it back up with fresh water. Some reservoir cats bowls automatically refill as your cat drinks.