One of the largest factors in assessing the quality of water is determining its pH levels:
Underwatered plants will develop dry and yellowing leaves.
Hard vs. Soft Water
Unlike agricultural crops, marijuana growers often grow their plants in remote, hidden places where access to water is limited or non-existent. When considering a potential grow site, proximity to a water source is important. Growers can test near-by streams and rivers before using their water for irrigation. Things to test for include pH balance, mineral content, contaminants, and pollutants.
One way of softening hard tap water is to dissolve water-softening compounds into the water. However, that isn’t the best way to soften water for marijuana plants because the softening-compounds are high in sodium. Sodium acts as a salt and collects in and around the plant’s roots. The accumulation of these salts disrupts turgor pressure, photosynthesis, and transpiration. I.e., a cannabis plant with high sodium deposit in its vacuoles will not transpire properly, which limits its ability to absorb water through the roots. Use reverse osmosis or charcoal filters in your watering system to prevent the minerals from hard water building up.
Water is an indispensable element during plant cultivation. Cannabis plants, especially seedlings, are sensitive to the water they receive, and specifically the water’s pH, contaminants, and minerals. Underwatered plants may become droopy and dry, while overwatered plants display yellow leaves and stunted growth.
Regular water comes in the choice of cold or hot water. Water coming from the cold tap is likely to include a lower count in relation to sodium and calcium build-up, and should also be clear of sediment if able to allow the cold water to run for a period of 25 seconds or so. A hot water tap is likely to include a lot of calcium, sodium, lead, and rust deposits. It is only necessary to use a sufficient volume of water in order to achieve the ideal temperature (70 to 80°F).
It is often reported by cultivators that plants are able to grow at a faster rate with the help of distilled or purified water. A reason for this might relate to the heavy metals (nickel, arsenic, lead, etc) and sodium often detected in hard water. Purified water is certain to be clear of these types of elements. Regular watering using hard water is likely to cause alkaline salt deposits in the medium which can have a negative impact on the beneficial minerals, and result in zinc, copper, and iron deficiencies. A variety of purified water options are available, but not all are entirely free of the minerals that might cause the build up of salt over the long-term.
It is possible to filter regular water using a charcoal or carbon filter which should ensure the water is left free of most large particles and chlorine, but still likely to include the solids like heavy metals and sodium.
Purified water is certain to contain sediment/carbon filtered water or reverse osmosis. In the process of buying store bought water you want to identify those marked Distilled or RO. The water could still include a small amount of heavy metals and dissolved solids similar to tap water.