Rats should have 24/7 unrestricted access to clean drinking water. Their drinking water shouldn't have anything in it, even vitamins. Vitamins aren't needed when you have a good diet, and medicine should not be put in bottles. It's an unreliable way of measuring and/or dosing and may lead to antibiotic resistance. All drinking water should be *non-*distilled water, plain, and with no extra additives.
To let your rats drink water, you can choose between either bottles or bowls. Bottles are upright containers with a "straw" coming off the bottom. Inside the nozzle is a small ball that rats push up and down to let the water come out. A con of bottles is there's a chance the bottle will malfunction, leading to either too much water coming out (leakage, really messy) or not enough (dehydration). However, a properly functioning water bottle won't be very messy and is pretty hygienic. Water bowls are also an option. It's better to opt for a bowl that attaches to cage bars. Water bowls allows them to use the water to play in, but it'll get everywhere. Bowls may also be the target of pee and poop, so they'll have to be cleaned frequently so the drinking water is healthy enough to drink. Either is fine, but water bottles will be the easier + more hygienic option.