How Important is Water Quality When Growing Cannabis?

Does Water Quality Matter?

Water makes up more than 70% of the planet, so it’s pretty important. But does the quality of water really matter when growing cannabis?

The short answer is… yes.

So, Why Does Water Quality Matter?

Not all water is created equal. The content of water from our faucets or hoses or rivers or lakes or rain barrels is more than simple hydrogen and oxygen.

Water contatins a wide variety of minerals and bacteria. Some of these are beneficial for healthy growth. Others are used to stop growth in its tracks. Think about how we use chlorine to prevent harmful protozoa/bacteria in our water.

Being aware of water content can go a long way. Not only in growing healthy cannabis crops, but staying healthy and hydrated yourself.

Something in the Water

Water is a major component in getting the proper soil pH balance. Purified water has a pH of 7 (which is neutral). Most tap water leans slightly alkaline (pH 8). Water from rain barrels, rivers, ponds, lakes, or certain wells, can lean toward the acidic side of the scale (pH 5-6). This is due to the quantity of selected minerals that make up or are broken down in a given water source. So when applied to the soil the water pH levels directly affects soil pH levels. Alkaline water can be used as a tool to balance soil with an acidic pH and vice versa. This can be very helpful in maintaining good soil and plant health.

Water content can be tested by the use of a simple water quality test kit. Which can be purchased online or from your local hardware store.

There are also visible, physical signs that indicate a change in pH levels. Yellowing of the plants leaves can be caused by a number of factors.

One is an abundance of calcium in the soil. This is commonly due to a higher concentration of calcium in most municipal water systems, or “hard water.”

What is Hard Water?

Hard water contains a higher concentration of trace minerals, such as calcium and magnesium. These minerals are picked up as the water flows over rocks and soil. Hard water typically has a pH leaning slightly alkaline due these mineral deposits. This makes hard water less than ideal for cannabis growth, in most scenarios.

Now, I know what you must be thinking. If there is hard water, is there soft water?

What is Soft Water?

Soft water has low concentrations of mineral ions, making it more neutral to acidic in pH. Soft water tends to have more salt content, although not high enough to be detrimental to human or plants.

Hard water can be conditioned to soft water by a few different chemical methods. This is not recommended for use on gardens with consumption in mind due to the addition of other chemicals to the water. Adding chemicals defeats the purpose of the entire process.

To restore the water back to a neutral pH after the chemical treatment is not cost effective in most cases.


So, How Does Water Quality Affect Your Plants?

Some growers recommend a soil pH level of 5.5-6. Others say pH 6-7 is ideal.

What is the difference and why does it matter?

The pH of the soil determines the amount of nutrients (vitamins and minerals) the plant can absorb at a given time.
The debate between levels is based on which nutrients the grower believe to be more important.

In hydroponic applications, cannabis root development tends to do better in the pH 5.5-6 range. This is possibly due to increased water absorption, as well as many other factors that go into soilless applications.

In soil, the roots perform better in the 6-7 pH range.

Regardless, the soil should lean slightly acidic for optimum root development and in turn growth output.

This is why water content is so important.

If the content of the water is alkaline, then the plant may develop nutrient deficiencies. This is due to an alkaline soil pH, and will not allow your plants to grow to their fullest potential.

How to Prevent Alkaline Soil:

There are a number of ways to reduce alkaline levels in soil, but here we’ll just cover reducing the alkaline pH in water.

Water Filtration

Filtration is done to reduce the amount of mineral concentration in water. This leaves it with a close to neutral pH (pH7). This is done one of two ways: reverse osmosis and distillation.

Reverse Osmosis

Reverse Osmosis is a process in which water is filtered to remove the majority of impurities including heavy metal, other minerals, and chemicals. This is done by reverse engineering the natural process of osmosis.

During osmosis, water moves from a high concentration of particles to a lower concentration of particles, in an attempt to balance the particles equally between two mediums.

The clearest example of osmosis is “pruney” fingers in a bath. The water concentration in the tube is higher than the concentration in the human body. This causes water to move from the tub, through the semipermeable membrane of the skin, into the fingers.

Reverse Osmosis uses pressure to move the water from a low concentration of particles to a high concentration.
Imagine if you could take a very deep breath during the bath, applying enough pressure to the skin cells that water could move from inside the fingers out into the bath. That is how reverse osmosis works.

The larger mineral particles (minerals/chemical) stay on one side of the membrane and pressure moves the smaller (water) particles out, creating purified water.


Distillation is speeding up the natural process of earth’s natural water cycle to filter out impurities. Unfiltered water is heated to a boil. The steam (which is pure oxygen and hydrogen) rises up and is moved to another container by means of tube or condenser coil. This return the particles from gas to liquid resulting in purified water with no trace minerals.

Tap Water pH Adjustment

If these systems are too costly for your current operation, tap water can be adjusted by using micro adjustment pH kits. These kits are how most hydroponic applications are maintained and can be a useful addition to any grow.

You can purchase them onlineor at your local hardware store.

Any of the above applications for filtering water and or adjusting pH can be an effective way in sustainably managing the pH of your grow system.


Yellowing Leaves or Chorosis

If you notice a yellowing on the tips of leaves or in erratic places on the leaves, try this.

Check the lighting source for over or under light exposure. If the other plants in the given area are healthy, re-test your water supply and soil for pH levels. Assure there is no calcium build up and that nitrogen lock out is not the issue.

If these levels are normal, a fungal infection may be the cause. You can treat fungal infections by moving the infected plant to quarantine and adding beneficial bacteria/protozoa to the soil (bacteria bacillus subtilis).

This is a naturally occuring bacteria than will break down the fungal growth. Fungal infections spread through spores and can be developed in areas where plants are overcrowded or humidity is too high.

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