Water should be provided all the time. You can use a bowl (which requires more frequent changing).
How Much Water do Rats Need?
The primary problem with bowls is that a) your rat can fall in, b) bedding, poop, food and all sorts can end up in there and c) it can spill making a huge mess.
There are also plastic water bottles available that can attach to the cage, however, some rats like to chew through it. I personally prefer buying the glass ones. It’s sturdier and doesn’t shift around as easily.
READ ALSO: Is My Rat Eating?
The 8oz water bottles will probably work for one rat but you’d be better off just getting the larger ones. I have a 32oz water bottle since it gets hot where I live and rats will drink more during the warmer days.