We also use our pond for the house water supply. I used Shore Klear on my cattails last year. According to the label as long as you do not apply it directly to the water you don't have a restriction for using it around a potable water supply. If you do spray directly on the water there is a 48 hr restriction. I think the secret was to wait until the seed heads emerge and then cut the heads off. Then spray and wait until they turn brown and lastly cut them off below the water line. I hope it works. I guess I'll find out this summer.