It seems to work depending on season
Reading the literature it seems that many cruisers collect rainwater. I saw a nice hard bimini that was rigged to collect rainwater. Basically there was a edge that directed water to a downspout. Then a hose was connected to the downspout and lead to the holding tanks. I am thinking that a cleaner arrangement would be a tarp rigged to collect water that is kept clean until water is needed. Our deck has a toe rail and all water goes through two drains. It would be easy to add a diverter valve to direct that water to the tanks. But this would require clean decks!!!! Of course if you expected a couple days of rain it would be no problem to let the decks rinse well before collecting water. But for collecting water from a 30 minute thunderstorm I think that my tarp idea would work better.