I live in California and save water that I run while I'm waiting for it to warm up (like for a shower or face wash). I also save the water I wash fruit and vegetables with. I put this water in my 30 gallon trash cans to water potted plants. I just purchased some stuff to kill any mosquito larva that might occur even though I keep the lids on the cans. The instructions are for sq feet and I have no idea how to measure this since my cans are rounded. Thank you for your help.