It's very normal to find a little blood around the vent shedding, that usually happens when snake's shed because there is also shedding in their vent so when they shed it off a little blood will be on the shedding but it's really nothing to be worried about. When my female sheds this happens as well, but it doesn't hurt her at all.

For the water, if it's clean and is fine for anybody to drink I'm sure your snakes will be OK drinking. If you want to make sure it's safe, like frankykeno said, you can test the water to be sure it's safe for your snake drink.