Today we begin a program of encouraging Vashon Island growers of all sorts of plants to use rainwater instead of water from the aquifer. In most cases, the pH of our water table is sub-optimum for plants and this is especially so for marijuana. The godfather of marijuana cultivation, Ed Rosenthal teaches that optimum pH for cannabis is 6.3 to 6.8 with a total hardness of 125-150ppm. The Vashon aquifer is 7.8 to 8.2 and 300ppm with some slight seasonal changes. This is simply more reason to use a rainwater catchment system to water your plants year-round instead of using the tap.