I’m not using a water bottle at the moment because I’m
always home, but when I do wash it every other day, same as cups. I specifically chose one that didn’t have a straw or any other hard to wash parts, and that has a wide enough opening that i can properly wash the inside.
It seems like a lot of them aren’t really designed to be cleaned, which is wasteful because people just use them until they get gross and throw them away. Probably worse than using disposables in some cases.