I give my rats distilled water. At the very least, it’s a good idea to give pet rats filtered water since chlorine and fluorine are both toxic for rats. If you choose not to give your rats distilled water, Britta filters work well for eliminating chlorine and fluorine.
I use glass water bottles inside my rats’ cage. You can tell your rat is getting water from their water bottle if, while they’re licking it, you see bubbles floating upward inside the bottle. Change their water daily and clean the bottles out well—at least once a week—with a bottle brush.
When my rats are out of their cage, I usually place a small glass bowl of water that’s not easy to knock over in the area in which they’re playing. It’s not a good idea to place a bowl or dish of water in your rats’ cage since they can easily drop food (or worse!) into the water and contaminate it. That said, if you’re able to place a water bowl on top of one of their boxes, this can work out well.