I personally don't usually get that much rain to worry about. But if it does rain, the little amount of water that makes it into my system and reservoir, is just that much less water I need to add/replace from what the plants drink up. And with the reservoir placed underneath a table or bench, very little rain water can make it's way inside from the reservoir itself. I also keep an eye on the 10 day weather forecast in my area at
intellicast.com (just put in your zip for your local weather forecast). If there's heavy rain forecasted, I just plan my
nutrient changes for after the heavy rains.