Have a similar problem and as I spent yesterday scrubbing mildew out of the tile grouting on the bathroom floor I definitely feel your pain (tiny tiles too so lots of grouting). All I can suggest is to try to keep it as dry as possible, even if it means giving it a wipe down before you leave the house for the day. Maybe clean the exhaust fan, hopefully it might work better. I used the shower squeegee to get the water off the floor this morning - it's a PITA but I'd rather do that than spend another Saturday scrubbing the floor! If you have old cloth nappies maybe just keep a couple handy and give it a quick once over before you leave so the water doesn't sit there all day.