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What’s the best water for growing plants?

Water plays a crucial role in sustaining life, especially for plants. However, when it comes to choosing the best water for growing plants, including cannabis, the quality significantly impacts the final outcome. Many individuals tend to use readily available tap water without considering potential consequences. Moreover, the common practice of adding various products to the water for plant nutrition without monitoring pH or EC levels can be detrimental. This approach increases the risk of plant illnesses, attracts insect and fungi infestations, ultimately affecting the quality of the harvested flowers. Therefore, careful consideration of water quality and proper monitoring practices are essential for successful plant growth.

What’s the best water for growing plants?

We’re going to go through a few different types of water that you can use when growing plants, whether they’re cannabis, flowers, aromatic or decorative plants .

Tap Water

Tap water is commonly used for watering cannabis due to its widespread availability. However, whether it’s suitable depends on your location, as water characteristics vary. Tap water can be categorized as hard (EC + 0.8), medium (EC + 0.4), or soft (EC – 0.4), with a generally alkaline pH over 7.0. It often contains additives like lime, chlorine, and fluoride, which can adversely affect soil life and quality.

To use tap water for plants, you can take certain measures. Allowing the water to sit for approximately 24 hours enables minerals and components to settle at the tank’s bottom. Alternatively, employing an osmosis filter helps purify the water, making it suitable for both human and plant consumption.

best water for growing plants tap water

Distilled Water

Distilled water, available in supermarkets and drug stores, is free from minerals and microorganisms, making it an excellent choice for plants. While safe for occasional human consumption, its lack of minerals makes it unsuitable for continuous use. When using it for plants, note that it typically has a pH above 7.0 and an EC of 0.0. To make it suitable for plant growth, adjust the pH and add calcium and magnesium until reaching a 0.4 EC.

Distilled water is produced through distillation, involving heating the liquid until it vaporizes. The vapor is then cooled to condense the water, leaving behind any other components that evaporated during the process.

Air Conditioner Water

Air conditioner water is taken from your very own air conditioner, and you can use this water when it comes to watering your cannabis plants, as it’s essentially distilled water, although we always recommend using an EC meter; depending on how old the AC unit is or its design, it may actually have an EC of 0.4 rather than 0.0. Its pH is usually over 7.0.

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Reverse Osmosis Water

Reverse osmosis water is a type similar to distilled water, although not entirely as pure, as it doesn’t eliminate 100% of all minerals and impurities in water such as lime and chlorine. You can easily obtain reverse osmosis water at home by installing a quality osmosis filter. Typically, osmosis filters produce water with less than 0.4 EC and around a 7.0 pH, making it suitable for both drinking and watering plants without requiring additional modifications.

Reverse osmosis water is achieved by using filters that capture minerals and other unwanted elements in the water. The purity of the water depends on the filter and its model, resulting in varying levels of purity.

Rain Water

Rainwater, collected directly from nature, is obtained by storing rain in tanks for later use. While it is generally not considered potable, some studies suggest otherwise. Nevertheless, it can be effectively used for watering various types of plants. As rain gathers, it naturally eliminates harmful elements, and since plants in nature thrive on rainwater, it is considered one of the purest fresh waters on Earth. Rainwater typically has a pH close to 7.0 and an EC no higher than 0.4.

To obtain high-quality rainwater, set up a water collection system that remains as clean as possible to avoid absorbing any elements that could compromise water quality. Consider installing an impurity filter for added purification. For optimal results, use rainwater collected outside of cities, as urban rain is often contaminated due to its descent through polluted environments.

rain water

Well, reservoir, spring water etc.

Water sourced from wells, springs, reservoirs, and similar outlets is not recommended unless its composition is known through a local study, detailing its mineral and chemical content. This knowledge is crucial because such water sources might have been contaminated with chemical insecticides or mineral fertilizers, rendering it potentially harmful for your plants. Additionally, these water types often harbor significant amounts of bacteria, fungi, viruses, and parasites.

To use this type of water, thorough preliminary study is highly recommended. If necessary, treat the water or prepare the storage area to prevent the spread of bacteria. For privately-owned wells, surface treatments like ultraviolet light or chlorine can be applied. In the case of springs, reservoirs, or public areas, contact the local authorities to ascertain water contents and take necessary actions if the water is unsuitable for plants or poses risks to the environment.

River Water

Using river water for watering plants or even drinking may seem like a good idea initially, but it’s not recommended. Rivers, often spanning kilometers, can have segments contaminated by pesticides, industrial zones, or factories discharging residues. They may also contain dead animals, leading to water contamination through decomposition.

While the location of a river can impart unique characteristics to its water, each river’s composition differs. Due to the presence of specific minerals, river water may not be suitable for cannabis cultivation, necessitating a comprehensive analysis beyond pH and EC.

To utilize river water, it’s advisable to reside in an area where the local authorities confirm the absence of contamination from human activities. If the water in rivers near or within cities is your only option, it’s highly recommended to avoid using it.

Bottled mineral water

Bottled water is obviously designed for people to drink, although it’s not the best option for cannabis plants. Still, it’s better than using unknown tap, river, or well water. Mineral water is guaranteed to contain no harmful substances, and its EC levels are lower than 0.5, with a pH around 7-0, although it may have high amounts of different minerals which may end up affecting how your plant grows and how the soil behaves, such as calcium.

water bottles

In order to work using bottled mineral water you need to choose a brand that has the lowest amount of minerals, and you need to adjust the pH and EC like you would with any other type of water; it’s easy.

The best water for growing plants

So, after going through various different types of water you can use when growing cannabis, here is our ranking of the type of water you should use for growing your cannabis plants:

  • Distilled water
  • Reverse osmosis water
  • AC Unit water
  • Bottled mineral water
  • Rain water
  • River water
  • Well, reservoir etc. water
  • Tap water

This ranking is of course just an estimate, and the different types of water mentioned in this post may vary in position depending on the irrigation supplies and their individual characteristics related to location and environment.

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Erik Collado

Con más de 10 años de experiencia en la industria del cannabis, sus experiencias y aprendizaje son la base del éxito de GB The Green Brand.

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