I can get quotes from jorges book as well as Mel Franks book stating exactly what Myoso just said , that a drop per gallon is safe and will benifit your plants water consumption by letting the water penitrate more evenly I know it sounds crazy but I have personal experience with this and I'll take Jorges and Mel Franks word over Frostdick anyday. Here is a quote from his book, "Since you want to wet the lower layers, you should thoroughly saturate the soil. If the soil is completely saturated, it should hold water for a minimum of a week. Usually only two or three waterings a month are required by a garden that is completely dependent on irrigation.
The most efficient way to water is to let the water slowly seep into the soil, so that all the organic particles which hold the water are saturated. If the soil is very dry, and the water beads or runs off and is not absorbed, add household laundry detergent at the rate of one or two grams per gallon of water. It acts as a wetting agent, which breaks the surface tension. Once the soil is treated with a wetting agent, it usually absorbs water throughout the growing season." And the website is
THE MARIJUANA GROWER'S GUIDE..........by Mel Frank & Ed Rosenthal its under the section called "Older Plants" Anyone who thinks they know what they are talking about should read up before they give out false info..