Growers often seek the purest water source for their Cannabis plants, believing that removing all impurities offers maximum control over their nutrient regimen. Purified water, such as that produced by reverse osmosis (RO) or distillation, has been aggressively stripped of its natural mineral content and contaminants. While this purification process appears ideal, water lacking dissolved solids presents unique challenges that must be expertly managed to ensure healthy growth.
Understanding Purified Water and Total Dissolved Solids
Reverse Osmosis and distillation are the primary methods used to create purified water. These processes force water through fine membranes or evaporate and recondense it, separating water molecules from almost everything else, including dissolved salts and solids. The resulting product is characterized by a measurement called Total Dissolved Solids (TDS), which quantifies the concentration of inorganic salts, minerals, and organic matter suspended in the liquid.
TDS is typically expressed in parts per million (ppm) or measured as Electrical Conductivity (EC), which indicates the water’s ability to conduct an electrical current due to the presence of these dissolved ions. Standard tap water often carries a TDS reading between 100 and 400 ppm, reflecting the naturally occurring minerals it has collected. In contrast, purified water from an RO system or distillation unit generally registers a very low TDS, often falling in the range of 0 to 10 ppm. This low measurement means the water contains negligible amounts of pre-existing compounds, fundamentally altering how it interacts with added plant nutrients.
The Impact of Zero Mineral Content on Plant Health
The most immediate consequence of using purified water is the absence of naturally occurring micronutrients that plants rely on for metabolic functions. Tap water frequently contains beneficial levels of calcium and magnesium, two secondary macronutrients needed for cell wall structure and chlorophyll production. When growers switch to purified water without supplemental additions, they rapidly face calcium-magnesium deficiencies, often called “Cal-Mag issues,” because these elements are completely absent from the water base.
Calcium deficiency can manifest as localized death of growing tissue and distorted new growth. Magnesium deficiency typically causes interveinal yellowing on older leaves because the element is mobile within the plant. These deficiencies occur because the purified water has stripped away these necessary elements, leaving the plant reliant only on the grower’s supplemental nutrient additions. Without a proactive supplement regimen, the Cannabis plant lacks the building blocks required for healthy cellular development.
The second major problem is the lack of buffering capacity in water with zero dissolved solids. Buffering refers to a solution’s ability to resist changes in pH when an acid or base is introduced, a property usually conferred by bicarbonate and carbonate ions. Since purified water has had these buffering agents removed, its pH is highly unstable and susceptible to sudden changes.
When concentrated nutrient solutions, which are often acidic, are mixed into unbuffered purified water, the solution’s pH can drop rapidly and dramatically. This rapid swing makes it difficult for the Cannabis plant to absorb nutrients efficiently, as each element has an optimal pH range for uptake. If the pH falls too low, the highly acidic conditions can lead to nutrient lockout, where elements remain in the solution but become chemically unavailable to the plant’s root system.
Essential Steps for Using Purified Water Successfully
To counteract the inherent deficiencies of purified water, the grower must first initiate controlled remineralization. This involves adding a dedicated calcium and magnesium supplement, often called Cal-Mag, before adding any primary nutrient mix. This targeted addition ensures the water base contains sufficient secondary macronutrients to prevent the common deficiency symptoms that arise from using zero-TDS water.
Following the Cal-Mag addition, growers should use a complete nutrient line specifically formulated for use with reverse osmosis or soft water. These specialized formulations provide the full spectrum of trace minerals and micronutrients otherwise missing from the purified water. Mixing the solution in this specific order—Cal-Mag first, then primary nutrients—is important for chemical stability and ensuring all elements are available for plant uptake.
Finally, the unstable nature of the water requires diligent pH management after all supplements and nutrients have been incorporated. The nutrient solution’s pH should be tested using a reliable meter to ensure it falls within the optimal range for Cannabis, typically 5.5 to 6.5 depending on the growing medium. Since the solution lacks natural buffering, growers must use pH Up or pH Down products to precisely adjust and stabilize the final mixture.