I just use water bottles the bigger 32oz ones. but my kitchen sink is 30 feet from the rats. so it's no big hassle to fill them every other day. i do it in kind of a routine. i fill a big pitcher with water then i check each tub and fill bottles as i go. check for who had new babies dead babies. give evryone a scratch on the head etc. then move on to the snakes open every tub check for messes. top up the snakes water and so on. so in my mind the water filling helps me keep a closer eye on things. because i need to check on them on a more regular basis.