Ed Rosenthal's Marijuana Grower's Handbook

Water

Not all water is created equal. When we drink different waters, we experience their distinctive qualities as different flavors. The mineral, carbon dioxide, and oxygen content of water vary substantially, and affect your plants. Three key measures of water composition are its alkalinity, its pH (alkaline-acid level), and its content of dissolved minerals. Mineral content is often referred to as dissolved solids, which are expressed as parts per million (ppm) and can be tested approximately by measuring the electrical conductivity (EC) of the water.

Alkalinity is the ability of the water to buffer acids. When water contains dissolved solids, usually calcium (Ca) and magnesium (Mg), its pH is not affected as much by the addition of acidic substances, such as a soluble fertilizer. The Ca and Mg buffer the acid/alkaline balance so that small additions of fertilizers don’t create dramatic changes in pH. When water is very pure and contains no minerals, it is called soft water and has little or no buffering ability, so its pH is very changeable. Adding a small amount of an acidic substance has extreme effects on soft water’s pH.

Waters from different areas vary dramatically in the amount of dissolved solids they contain and, consequently, in their buffering ability. For example, tap-water in San Francisco, California contains about 65 ppm of dissolved salts. It has very little buffering ability. By contrast, water in Los Angeles, California contains about 450 ppm. This úhard waterî has very strong buffering ability, so it takes a large amount of pH adjuster to have much of an effect.

Water districts and companies continuously test the water they supply you. The test results are public records and are available from the water district or company. The results may be sent to customers annually or posted on the Internet. If not, they can be obtained by communicating with the water supplier. In addition to measures of alkalinity, dissolved solids, and pH, the report shows contaminants.

A reading of 125-150 ppm for your water is a good starting point because it represents some buffering ability, but not so much that large amounts of minerals have to be added to adjust pH. To increase the reading use Cal-Mag, which contains a solution of calcium and magnesium, or alternatively, calcium nitrate (CaNO3). To lower the mineral level in the water, use a reverse osmosis system or a charcoal/chemical de-ionizer. The high-mineral water can be mixed with the purified water to get to the desired 125 ppm.