If you're only interested in measuring increase over time, then the only assumption you need to make is that average consumption of Ace-K remains constant over

If you're only interested in measuring increase over time, then the only assumption you need to make is that average consumption of Ace-K remains constant over time. And, I suppose that people that consume Ace-K pee in pools at the same rate as other people. As someone who doesn't pee in pools (but has peed in the ocean), I don't know how valid that is.