Various methods can divide cannabis plant material into parts, or extracts, that contain different chemicals. With cannabis, extraction techniques are often used to isolate specific desirable compounds, and cannabis contains at least 113 cannabinoids, including cannabidiol (CBD) and tetrahydrocannabinol (THC).

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Many critical decisions go into choosing the optimal layout, lighting plan, irrigation/fertigation systems and climate-control design for a successful hydroponic cultivation facility. These highly engineered systems make up a large portion of upfront build-out expenses. However, all too often, the importance of a consistent, reliable water source is overlooked. Even seasoned professionals can lack the adequate knowledge to respond to increasingly complex water issues that can determine the success or failure of an operation.



Here’s the upshot: Starting out with a base of pure water ensures a consistent feed formula with repeatable results for every crop cycle, regardless of source water quality.

The most efficient and cost-effective way to ensure a reliable source water profile is a commercial-scale reverse osmosis (RO) system. While RO as a requirement has been subject to debate, today’s commercial-scale cultivation professionals know it’s the single most affordable and least energy-intensive technology to produce pure water.

To be clear, not every situation requires RO. In a best-case scenario, reliable, consistently high-quality source water is readily available. However, if water needs to be treated, RO becomes a logical choice for the serious grower.

For modern growing practices, it’s particularly important to highlight the differences between industrial agriculture and cultivating a refined, premium product on a commercial scale. There are many methods and technologies shared by the two, but the most important difference is that Big Agriculture is primarily concerned with volume, not quality.

Volume vs. Quality

Producing a top-shelf product — whether it be orchids, craft beer or exceptional cannabis — requires full control of inputs, including water. Furthermore, the medical cannabis community is becoming increasingly aware that a pure product requires pure inputs, water being one of the most critical. Avoiding tissue contamination can only be achieved by scrutinizing every stage of the production process, from cultivation to packaging.

Certainly, volume is extremely important. It makes sense that agriculture professionals are beginning to have tremendous influence over how large-scale cannabis grow operations are designed. But achieving volume is relatively easy with cannabis, whereas growing a high-quality product requires a well-rounded, refined approach to success.

Those with experience in industrial agriculture growing tens of thousands of acres of a monocrop may be skeptical of the use of RO to purify source water for commercial cannabis cultivation. Because the volume of water needed for industrial agriculture operations is much too great to purify with RO, those operations typically rely on customized nutrients based on the contents of their untreated irrigation water.

This may work to produce a decent yield from a traditional monocrop, but when controlling unique, strain-specific environments and nutrient formulas for a high-value crop such as cannabis, every input can affect the final value of the product. The goal of commercial cannabis cultivation is to produce the best quality and largest yields from the given square footage of canopy space and to maximize efficiency in these environments. Large-scale, traditional agriculture water treatment practices do not always apply to specialized, high-value crop production.

A garden attendant waters plants, while water-mats keep excess waste to a minimum. Photo by Inae Bloom.

Frequently Asked Questions

How does one use RO water correctly?

Cultivators use RO water as a pure base to mix with their nutrients. Experienced growers using RO water know it’s necessary to first add the desired amount of plant-specific, bioavailable calcium/magnesium, then the chosen nutrient regimen in order to achieve optimal, consistent results and to avoid plant deficiencies. The correct mix of specialized nutrients and minerals is an essential component to ensure fast and healthy plant growth.

A majority of total dissolved solids (TDS) in untreated source water are made up of calcium and magnesium (also recognized as hardness), two beneficial minerals that are vital to the growth of plants. Although calcium and magnesium are necessary for plant growth, the calcium carbonate and magnesium carbonate molecules typically found in source water are too large for plant roots to absorb efficiently. Therefore, these compounds need to be chelated (broken down) into a more usable form, requiring extra energy from the plants that would be better spent on reaching their full growth potential.

Adding chelated calcium and magnesium (as well as beneficial biologicals) to RO water is the most efficient and measurable way to give plants what they need to thrive.

Do RO systems waste much water?

All RO machines have a feed water inlet, a purified product water stream, and a waste water stream. The RO membrane acts as a barrier to all dissolved salts, minerals, inorganic and most organic molecules. Pure water molecules pass freely through the membrane, creating purified product water (or permeate stream). The rejected contaminants are concentrated in the waste water (also referred to as the RO concentrate).

While it is true that all RO systems have a certain amount of waste water, the technology has evolved greatly through the years, and today there are ultra-efficient RO filters capable of producing up to a 4:1 ratio of product water to waste water. Historically, that ratio had been reversed: one part product to four parts waste.

Commercial RO is also integral to reclamation systems that recycle nutrient runoff water. As volume usage limitations and waste water regulations become more rigid, a sustainable water treatment plan is becoming an increasingly important part of a professional cultivation operation’s initial design. These regulations are imminent and it’s crucial for business owners to be aware of these new laws and have a plan of action to be legally compliant.

Do RO systems produce water too slowly?

Operations that use a commercial RO system are typically designed with large, pure-water storage tanks. The RO system is sized to provide the daily demand for water that will later be distributed to nutrient mixing reservoirs. An RO water storage tank allows facilities to have a reliable, on-demand water source versus distributing water straight from the RO system.

On the hobby hydroponics scale, RO systems typically produce 75 to 300 gallons per day (GPD). A 300-GPD system will produce 12.5 gallons in one hour. However, there are high-flow commercial-grade RO filtration systems capable of producing up to 100,000 GPD or more. The more filtered water per day a system can produce, the higher the flow rate will be. For example, a 10,000-GPD RO system can produce water at 416 gallons per hour. The larger the RO system, the more quickly it will produce pure water.

Will using pure water really affect my results?

Every properly controlled input has the potential to improve yields. Most nutrient manufacturer’s feed charts assume a base of pure water. By starting the feed formula with RO water, growers are able to dial in exactly what they feed their plants. For the serious cannabis professional, the guesswork of what might be in the water should be eliminated.

Purifying source water changes its base profile from a variable to a constant, maximizing a controlled operation’s potential success. Incremental gains in yield and quality can be crucial in today’s increasingly competitive marketplace. Starting with pure water removes water quality issues from the equation and ensures a consistent feed formula for plants which leads the way to reliable harvests.

Will carbon filters reduce TDS?

There is a common misconception that carbon filters can remove TDS from water. This is simply not true. While carbon filters will remove chlorine, chloramines and certain other toxins from water, they are not intended to remove any other dissolved minerals, and will not significantly lower the PPM count or electrical conductivity of the water.

Why does pure water matter?

Pure water plays a crucial role as the basis for a proper and consistent nutrient formula. Rarely do cultivation facilities have high-quality water straight from the tap. While most professional grow operations now use some form of water filtration, some still do not, and they are taking a major risk, especially if they are not fully aware of source water quality issues and how they might affect plant yields.

Getting a water test is of utmost importance to determine what levels of these pollutants are present. Too much hardness, iron, manganese, lead, copper or zinc in untreated source water can lead to lockout and deficiency problems. Chlorine and chloramines, typically added to municipal water, effectively kill any beneficial living microbiology. Fecal coliform, herbicides, bacteria, pesticides, phosphates and nitrates are, unfortunately, all too common in a growing number of water sources.

Fortunately, there are technologies available today to deal with even the dirtiest of water problems. The budget for an integrated water filtration solution is typically a small expense relative to the overall cost of building a facility. However, the small investment in reliable water quality can yield tremendous return. At the end of the day, developing an effective water treatment plan can help maximize a cultivation operation’s competitive edge.

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