Water quality is a frequent subject of debate among cannabis growers. Distilled water (DW) is processed by boiling it into vapor and condensing the steam, resulting in ultra-pure Hâ‚‚O with nearly all impurities removed. While this purity offers benefits, it also means the water lacks essential plant nutrients. Successfully using distilled water requires balancing the benefits of complete control with the drawbacks of missing these necessary elements.
Defining Water Purity and Total Dissolved Solids
The technical quality of water is measured by its content of dissolved substances, quantified primarily by Total Dissolved Solids (TDS) and Electrical Conductivity (EC). TDS measures the combined content of inorganic minerals, salts, and organic contaminants, expressed in parts per million (ppm). EC measures the water’s ability to conduct an electrical current, which relates directly to the concentration of dissolved ions.
Distilled water is defined by near-zero readings for both metrics, typically having a TDS level of 0 to 5 ppm or less. This high purity provides a clean slate, contrasting sharply with standard tap or well water. Tap water often contains unknown and fluctuating levels of minerals, with an EC typically ranging from 200–800 \(\mu\)S/cm.
Distilled Water and Essential Mineral Deficiencies
While distilled water eliminates contaminants, it also strips away minerals that cannabis plants require for healthy growth. Cannabis relies heavily on a full spectrum of macro and micronutrients, including trace minerals often present in untreated water. Water sources are often a natural supplier of Calcium (Ca) and Magnesium (Mg), which are secondary macronutrients plants need in significant amounts.
When a grower uses distilled water without adding supplements, the plants rapidly develop a deficiency in these two elements, often referred to as CalMag deficiency. Symptoms of this issue include the appearance of brown or bronze spots and splotches on the leaves, along with yellowing between the leaf veins. The absence of calcium can also lead to weak stems and poor root development. Therefore, using distilled water necessitates that the grower precisely measure and add back all necessary nutrients, including a CalMag supplement, to create a complete feeding solution.
pH Control in Cannabis Cultivation
A primary advantage of using distilled water is the control it grants over the nutrient solution’s pH level. Distilled water is inherently neutral or near-neutral, typically having a pH around 7.0. Its lack of dissolved solids means it has almost no buffering capacity, which is the ability to resist changes in pH when acids or bases are introduced.
This absence of buffering agents is highly advantageous because it allows the grower to fully dictate the final pH of the nutrient solution after adding fertilizers. Cannabis plants require a specific, narrow pH range for optimal nutrient uptake: typically 6.0–7.0 in soil and a more acidic 5.5–6.5 in soilless or hydroponic systems. If the pH is poorly regulated, the plant can suffer from “nutrient lockout,” a condition where nutrients are present but cannot be absorbed by the roots. Starting with pure, unbuffered distilled water simplifies the adjustment process, minimizing the risk of lockout.
Common Water Sources for Cannabis Growers
Distilled water is one of several sources growers consider, each with trade-offs in cost, purity, and convenience. Reverse Osmosis (RO) water is another popular purified option, which uses a filtration membrane to remove up to 99% of contaminants, resulting in a water quality very similar to distilled water. Like distilled water, RO water requires the addition of CalMag and other nutrients to be a complete feed solution.
Tap water is the most accessible choice, but its quality varies significantly by location, often containing chlorine or chloramine, which can harm beneficial soil microbes. High TDS in tap water can also make it difficult to calculate nutrient additions without risking nutrient burn or salt buildup. Rainwater is often considered an excellent natural source due to its low TDS and slightly acidic pH, but its purity can be compromised by environmental pollution, necessitating testing before use. Ultimately, while distilled water offers the highest degree of control for sensitive systems like hydroponics, its requirement for constant and precise mineral supplementation makes it a choice best suited for growers with advanced knowledge and specialized nutrient regimens.