Preparation of Water for Irrigation of Cannabis

Not only it is important to have enough water to irrigate your plant but the water also has to be pure. Normal tap water or well water is not clean enough for that. It contains dissolved gases, chlorine, cations, anions, and solids.

Water quality is assessed according to 3 criteria:

  • Acidity (pH);
  • Hardness;
  • Organoleptic properties.


The acidity of water determines the ratio of hydrogen and hydroxyl ions in it. If positive hydrogen ions prevail, it will be an acidic environment. Its value is measured from 1 to 6.9. If the solution contains more negative hydroxyl ions, then it will be alkali (measured from 7.1 to 14). In pure water, the balance between positive and negative ions is balanced and, therefore, it has a neutral pH (pH=7).

Acidity of Water
Acidity of Water

The pH level affects the plant’s ability to absorb nutrients and minerals that are essential for healthy growth and development. All plant species have their own optimal pH value at which they properly absorb the needed substances.

The optimum pH for watering cannabis is 5.5-6.5.

Download our free Grow Bible for more information about watering your marijuana plants.


Water hardness stands for calcium and magnesium ions in water. It is measured in milligrams per liter (mg/l). The increased level of calcium ions in irrigation water disrupts the absorption of important nutrients by the plant. A clear sign is the formation of a white crust on the surface, i.e. the water you use is too hard.

Hardness of Water
Hardness of Water

The hardest is the water from the wells which contains a lot of impurities. Its hardness index is usually 8-10 mg/l. Relatively low hardness is considered to be 3-6 mg/L. The softest water is considered to be rainwater or meltwater. Not in industrial areas, though. Its hardness is close to zero.

According to this article at the homedweller, for marijuana irrigation, it is desirable to use water with hardness less than 3 mg/l, but 3-4 mg/l value is also acceptable. 

Organoleptic properties

Organoleptic properties
Organoleptic properties
  • Transparency is the most obvious indicator of water purity. It depends on the amount of mechanical or chemical particles in the liquid. The fewer impurities in water, the cleaner it is. The cleaner, the more transparent.
  • Color. Water is inherently colorless. If it has any shade, it indicates the presence of foreign matter in it. Yellow indicates that it has iron salts and decay products, green indicates the presence of microalgae.
  • Smell. One of the peculiarities of pure water is the absence of smell. The presence of any smell indicates that it has biodegradable products or chemicals. Tap water may have a chlorine smell which makes it unacceptable for irrigation. And when you smell hydrogen sulfide, you can say that it clearly has pathogens.
  • Taste. Taste qualities of irrigation water do not play any role, but the presence of foreign flavors can be judged by the presence of impurities in the water.
  • Temperature. Any plants, including cannabis, are only watered with the room temperature water. Low or high water temperature can damage the roots. It is also not allowed to water the plant with boiled water because it has no oxygen in it which is important for the root system.

Methods of water treatment


It is the easiest, fastest, and free option. It is enough to collect water in a suitable amount and leave it for about 1-2 days. This will result in chlorine (present in tap water) escaping from it, and all the heavy impurities settling down.


Cannabis water can be cleaned with ion exchange or osmotic filters. However, water filtration is very time-consuming, especially with high amounts and low-quality filter water. It also involves financial costs, as the filters must be changed regularly. But this method allows you to purify the water from impurities and soften it almost completely.


The freezing method is only beneficial if it is correctly applied. Clean water starts to turn into ice at a temperature of 0 degrees, and water with impurities “needs” negative temperatures. Therefore, when the temperature goes below zero, all the frozen water is drained (since it contains impurities). And the rest of the ice is turned into melted soft water.

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Peat adding

Once in the water, peat acidifies it, absorbs heavy metals, and saturates humic acids. The color of the water becomes yellowish. Peat is poured into a bag which lets water through, after which it’s immersed in water for several days. 100 g (3.52 oz) of peat have to be added to 10 (338) liters of water.

Acid adding

If the water hardness is too high or the soil is too alkaline, citric or oxalic acid can be added. This increases the acidity and stabilizes the pH value. 2 grams of oxalic acid are added to 10 liters of water. The exact amount of acid required can be calculated by measuring the pH of the water by adding acid gradually.

Grow bigger and healthier buds with good water

Testing your water is really helpful in order to get the results you want. Growing marijuana isn’t hard, as long you use the right products. That includes pure water! Make sure your water has enough oxygen and not too much foreign matters in it. I would really recommend to get one of these test kits, so you know for sure your plants get what they need!

Avatar for Bob ILGM


Writer, Grower

Bob knows a thing or two about growing at home. He's not as experienced as Robert, but he has a knack for keeping his gardens ... See profile

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