I used to be accused of not drinking enough water when my veins were getting jack of being punctured. Didn't make a scrap of difference if I gulped down litres or not. I know lots of people believe in flushing out chemo. Fair enough. But I wanted it to hang around long enough to be effective too. I think there is a difference between insufficient hydration and overworking the bladder. But.....you have to drink a ridiculous amount of water before it will actually do harm. So follow your inclination.