Hi all - I have a metal 2 gallon waterer for my three girls. I keep it in the run next to the door so I can access it easily. Because it's pretty large, I generally only change the water once a week. Plus, we've had a ton of rain so the trough essentially refills itself. Our temps have not gotten over 80 yet this season so I'm not concerned with evaporation. My question - do I need to change and refill more than once a week?