i just had one being chewed on last night. only 5 mice in 10 gallon checked everything and the water bottle was plugged i hit the Lil ball 6 or 7 times no water came out so i took it out gave it a good squeeze and finally water squirted out. so since it took having to squeeze it to get water out cleaned it out with boiling water and a Lil bleach and it's worked fine since

mouse didn't look that bad at first looked like a cut kind off but took him out and checked he has a section of fur bout 1/2"x1' they chewed on fur was still connected but could literally flip it over so had to smack him in back of the head and kill him didn't want to take a chance of him getting some kind of disease

might want to check the water bottle cause once i put mine back in after cleaning mine went nuts to point they were fighting for who was going to drink first