Technodoll--if you rat-proof your coop, you can keep food and water in the coop at all times. Rat proof = no holes wider than 1/2", hardware cloth on all vents, etc...BTW the aforementioned client, HAS an exterminating company (and not a bad one) that comes by on a regular basis. I discussed rats with him recently--and as he said, there is just NO WAY to completely get rid of rats if you have them in the area. The best thing you can do is not provide them with shelter (buildings, brush, accessible compost bins, etc..) and not leave any kind of food or water around (bird feed, leftover tree fruit, accessible garbage). Preventing physical access is the best you can do.