3 Steps to Ensure Water Quality for Greenhouse Crops

Water media filter in a greenhouse

Media filters (commonly referred to as paper or fabric filters) can help remove organic debris in the solution, which will interfere with sanitization.
Photo by Rosa Raudales

Treating irrigation water is a risk-management strategy that should be in place in every greenhouse. However, before greenhouse growers choose their water-treatment system, they need to understand the quality of the water source, the treatment options that match the target issue, and the compatibility of a system with the operation’s practices and personnel. Here is an overview of how to choose a water treatment system. Note: this article does not cover water-quality issues related to plant nutrition.

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1. Test the Quality of the Water Sources

Water sources differ in quality, so the treatment choice should aim to manage the parameters that pose a risk to crops or irrigation delivery systems. Chemical, microbial, and physical parameters determine the suitability of water for irrigation.

Growers should test the quality of the water source and then use the results of the analysis to help select or refine treatment options. Initial testing will be an indicator of potential problems. For more information about interpreting water quality tests, you can use the WaterQual web tool at CleanWater3.org/wqi.asp.

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The quality of water can change unexpectedly. For example, drinking-water treatment facilities can increase the amount of fluoride or chlorine bleach up to 4 ppm — within EPA standards, but too high for most crops — without notifying the end user. Agrichemicals or nutrients can increase in surface water or ground water when agricultural runoff increases in water bodies that are connected to the water source. Plant growth regulators can leach into the solution and accumulate in the catchment tank. Therefore, growers should think about water treatment as a risk-management strategy and implement an approach that consistently monitors for potential risks (e.g., inline chlorine meter) or that has a continuous treatment point in place as a preventative mechanism (e.g., carbon filtration). The goal is to have a proactive approach — never a reactive one.

2. Match Treatment Options to Potential Problems

Multiple options are available to treat problems in water. Sanitizers tend to be the most difficult water treatment to select. The efficacy of sanitizers varies by organism (for more information about the efficacy of the sanitizer by target organism, go to Waterborne Solutions at Backpocketgrower.com/waterbornesolutions.asp). Sanitizers also differ in their residual activity or how much control they provide throughout the irrigation. Point treatments — i.e., ultraviolet (UV) light and heat treatment — control organisms when the solutions are in direct contact with the treatment system, and they leave no residues in the solution.

In contrast, injectable sanitizers continue to react throughout the irrigation. The residual activity of the injectable products varies by the inherent properties of each product and the concentration applied. The benefit of residual activity is sustained control throughout the system; the disadvantage is the risk of phytotoxicity when the product is applied at high doses or if it accumulates in closed-loop irrigation systems.

Plant pytotoxicity symptoms

Phytotoxicity can be caused by spilling of concentrated sanitizers.
Photo by Rosa Raudales

We must always keep in mind that even though we are treating water, our main objective is to grow crops and to do it effectively. Water treatments are only one component of the production process, and any other practices that can help prevent problems are integral components of the overall system. That is to say, if we want to prevent diseases caused by waterborne pathogens, we should think of the water treatment as a strategy to help reduce the inoculum from the water. However, we still need to prevent the entry of pathogens from other sources (e.g., infected cuttings or liners), avoid conducive conditions that promote disease (e.g., overwatering), rotate fungicides, and use resistant cultivars, when available. Another instance would be to understand that while filters remove debris or agrochemicals from the solution, we should avoid littering the solutions.

3. Think About an Integrated System Design and Monitoring

Consult an agricultural engineer to help you finalize the design. A few general tips:

  • Filter first, sanitize later. Organic debris in the solution will interfere with sanitization. Hence, filter out the debris before sanitizing.
  • Storage tanks will slow down the water flow and reduce the size of the equipment needed to treat water. The contact time of the sanitizers with the solutions can be extended in storage tanks, reducing the need for a high concentration of sanitizers.
  • Multiple-stage filtration is important. Growers abandon filters that clog too quickly. If they are clogging, they are capturing something. Install filters in series, from coarse to fine pores, to improve filtration efficiency and reduce the need of cleaning filters too often (if possible, use filters with automatic backwash).
  • Monitor, monitor, monitor! A system will only be effective if it is functioning properly. Include sampling valves to take samples or inline meters to measure active ingredients. Train your staff on how to monitor and adjust the system.

Finally, make sure the technology is a right fit for your company. I always recommend that growers speak with other growers about how effective the systems are, the service the companies provide, and how easy it is to manage. Many growers like high technology options, but many prefer simplicity. Both options work, just make sure it works for your team.


Potential Risks By Water Source 

While the exact characteristics of water sources will differ by location, we can generalize the potential problems that we can anticipate by source. 

Water Source  Potential Risks 
Drinking water from public watertreatment facilities  Chemical: High concentration of chlorine and fluoride. The EPA allows chlorine bleach and fluoride residues up to 4 ppm in drinking water. Most container-grown crops tolerate up to 2 ppm chlorine and fluoride (may be lower in young plants).  
Shallow wells  Chemical: High concentration of pesticides, herbicides, and fertilizers 

Microbial: Presence of plant pathogens 

Physical: Sediments, if there are no groundcovers in surrounding areas 

Deep wells  Chemical: Precipitates from iron, manganese, and calcium  

Microbial: Ironoxidizing bacteria  

Physical: Sediment 

Rainwater and reverse osmosis-treatment   None. The quality of rainwater is very high. However, microbial load or physical solids may accumulate in storage. 
Recirculated water   Chemical: Agricultural runoff can carry pesticides, herbicides, fertilizers, and plant growth regulators. 

Microbial: Plant pathogens, algae, and biofilm 

Physical: High amount of organic suspended solids 

Surface water (natural streams, rivers, lakes, and ponds fed from ground water springs, runoff from adjacent land, and rainfall)  Chemical: Agricultural runoff can carry pesticides, herbicides, fertilizers, and plant growth regulators. 

Microbial: Plant pathogens, algae, biofilm, and human pathogens 

Physical: High amount of organic suspended solids 


Water Treatment Options by Target Problem 

Multiple options are available to treat problems in water. Deciding between options requires a combination of technical and financial comparisons. 

Problem  Water Treatment Options  Objective 
Microbial:
Plant pathogens, biofilm, and algae 
Sanitizers: chlorination, activated peroxygens, ozone, UV light, heat treatment, chlorine dioxide, copper, etc.  Reduce inoculum.  

Remove established populations. 

Chemical:  

High concentration of salts 

Adjust nutrient program or pH 

 

Reverse osmosis 

Manipulate chemistry to make it suitable for plants. 

Remove high concentration of ions. 

Chemical:  

Agrochemicals 

Carbon filtration or ozone  Remove agrochemicals from water. 
Physical: Suspended particles   Filters: screen, disc, media, or membrane filters  Remove debris. 

 

Author Note: This work is supported by the Foundational and Applied Science Program (Critical Agricultural Research and Extension grant number GRANT11947449) from the USDA National Institute of Food and Agriculture. 

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