Mark Doherty   |   August 02, 2018

Designing a Water Reclamation System for Indoor and Greenhouse Facilities

Whatever the method, implementing comprehensive water management provides huge advantages.
Mark Doherty serves as the vice president of cultivation technologies at urban-gro, a leading cultivation technologies company delivering best-in-class systems, design services, and technologies to large-scale cannabis cultivators throughout…

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For today's commercial cultivator, there are a myriad of technology solutions. Of those, few are more complex than water management. The choices impact both the facility itself and the surrounding community. It is one of the areas that is particularly important to local regulators. If not handled properly, it can be damaging to both the crop and the environment.

The good news is that it is typically not one of the larger of a cultivator's operating costs. There are several strategies and technical solutions that cultivators can use. You want to think about how to prepare water before it goes to the plants. Then how you want to re-use and re-claim the majority of the wastewater. You also want to ensure waste product complies with local codes on water management.

A truth we must face as an industry is that cannabis cultivation creates a lot of wastewater. Many cultivators flushed this wastewater into local water systems or drainage fields. Now local regulators are rewriting regulations and are stepping up their enforcement. This shifting landscape of rules means water management is more important than ever.

Water management, from its source to its exit, needs a cultivator's full attention. Knowing water is a valuable resource and treating it as such, will lead to greater success. Cannabis is a much higher value crop than traditional agricultural crops or floriculture. Thus how water is treated upon entry to a facility requires even more care. Making sure the water is optimized before it reaches the cannabis plant is essential. This means that it doesn't contain any harmful elements and is the right pH and temperature.

Equally, the water needs to be managed after it has been applied to the crop. By this time it is mixed with run-off nutrients and pesticides as well as plant drainage waste. Water at this stage, can be reclaimed or disposed, depending on cultivator preferences.

We find that it only takes one crop failure due to contaminated or inconsistent water quality to make a grower wish they had a more sophisticated and bio-secure system. This is especially the case with condensate reclamation systems, as it is very likely the “dirtiest” water in the facility. Additionally, while effluent with a nutrient load can be reused and recycled, say in a batch tank system, it is prone to the same cross contamination issues and will eventually need to be dumped.

Investment in the right water management technology is the best way to get ahead of problems. It reduces risks to crops and makes you compliant with local regulations. It is not only the right thing to do, it also makes you a good neighbor.

Before you select water reclamation systems, there are a few things to consider:

  • Size of the facility - You need to know how much canopy what space is available for storage tanks and equipment.
  • Irrigation architecture - Batch tank versus inline fertigation? Flood and drain v. drip irrigation? Each of these choices impacts  water reclamation for both leachate and condensate
  • Growing media – Rockwool, coir, peat? What the plants are growing in will impact the amount and quality of effluent
  • Environmental conditions – Both inside and outside of the structure. It can impact water source, contaminants, and temperature. It can also include water conservation efforts, especially in high drought zones.
  • Compliance/regulations - How much, if anything, can we put down the drain? Often we can put something down there, but not everything. This can dictate how we design the system.

Once these variables are taken into consideration, we can begin to design the system. Done properly, cultivators can reclaim upwards of 80 percent of the irrigation effluent utilized, cutting back on cost and waste. Good condensate systems can capture almost 98 percent and re-use this as fresh clean water.

Lastly, I am not a believer in the myth of the "closed loop" which is often discussed. Based on my experience over the last 8 years designing these types of systems for various cultivation styles including aeroponic, aquaponic, and more traditional growing methods, I have yet to see a system that doesn’t have some kind of input and output cycle.

Additional Components

Here are some of the components necessary for effective water reclamation and remediation systems for a typical facility.

UV Sterilization System

This is potentially one of the most critical elements of a water reclamation system, as spreading contaminants via irrigation or condensate is an easy path to crop failure. One approach involves water running through tubes with high-intensity UV lamps in the center. As the water flows through the tubes, the light kills the microbes present. 


Ozone (O3) may be used to oxidize water, which is effective at killing microbes. This may be used both in the final “clean up” of the effluent before returning to fresh water supply and/or in the holding tanks prior to processing. An added benefit to the use of O3 is the conversion back to O2 increasing the dissolved oxygen level of the water.


It should be noted UV Sterilization Systems and Ozone require additional equipment to make them work. Tanks, pumps, and sensors, are all required to capture, shuffle, clean and reuse waste effluent of any kind. One of the issues we see with deploying these types of systems in existing facilities and new builds is a lack of space to hold the necessary tanks. The tanks can be quite large.

Discharge Tempering Systems

Many communities regulate the discharge of effluent from cannabis cultivators. They regulate the quality and quantity of the discharge. Municipalities allow for some discharge as long as it meets their standards. I like systems that reduce the levels of salts and improve biochemical oxygen demand (BOD) before water discharges into the sewer. These systems can use sensors and data logging. They are able to provide reports on EC, pH, volume and other parameters as needed.

Reverse Osmosis Systems

Reverse Osmosis (RO) removes inorganic solids (such as salts) from a solution (such as water). This is accomplished by pressure pushing the water through a semipermeable membrane. Some argue RO systems are wasteful. Yet keep mind today’s systems are more efficient than ever and getting better all the time.

Leachate Remediation Systems

Leachate is where water percolates through a solid and leaches out some constituents. It is possible to use RO treatment to remove the nutrient load. But, RO does not deal with other contaminants which may be present in the returning effluent. Before re-entry into the existing fresh water supply it help to clean and sterilize the water.  I like a customized multi-stage filtration system that has a small RO component to do this.

Making the Right Choice For Your Facility

Once you’ve decided on the elements of your system, you need to determine how it will be installed. There are two separate approaches to building reclamation systems. First, you can turn to a partner that will design a system that comes pre-wired and configured. This one is ready to plug into your facility. The other approaches involves building your own using a variety of disparate solutions. Both can work. In the latter, you need to ensure you have the appropriate in-house expertise. Either of these systems need to be built to handle capacity at peak loads. They should also be able to cover a variety of safety scenarios. Lest not forget, in either scenario, accidents and breakage can happen.

Regardless of what you choose, implementing comprehensive water management is a great idea. Water reclamation itself is a “must have” as part of any indoor or greenhouse facility that is regulated on effluent discharge. Overall, these systems help cultivators reduce risk, cost, and follow local regulations. It also contributes to a higher quality product, which after all is the final goal.