This is the 6th article in a series about water sanitation. The goal of this series is to get you reflecting on your own irrigation system before a problem occurs. 

If you’re following our series on water sanitation, you saw that previous posts covered where problems are likely to occur in your greenhouse, the types of pathogens found in water, where and how to sample your water and getting and interpreting a DNA test for pathogens in your water.

This post covers water treatment options, and was written by C. Dayboll with input from Phytoserv and Soil Resource Group.

Water Treatment Guide for Greenhouses and Nurseries

If you don’t currently treat your water it may be time to seriously consider a treatment system. Along with sourcing pathogen-free cuttings, making sure your water source and water-holding tanks are problem free, and practicing good sanitation in your greenhouse, water treatment to reduce pathogen loads is an important step to reducing loses from fungal and bacterial diseases.

Looking into water treatment technologies can be overwhelming, though, as there are many options out there and you need to consider your operation specifics. Add in the initial and ongoing costs, and the decision can be a complex one.

A few years ago, our friends at Flowers Canada Ontario (FCO) and the Soil Resource Group (SRG) came up with a guidance document to assist growers in choosing water treatment systems. It covers why you might want to treat your water and which systems are best for common problems like sediment, fungi, viral or bacterial issues. It also addresses costs, installation, space requirements and maintenance considerations.

In this post, we have identified things to consider before moving forward with an installation and given information about four commonly chosen water treatment options for consideration.  For more information, please check out the guidance document or contact the authors or a water treatment specialist.

Treatment Options:

Considering these parameters for your farm, you might need a fairly simple solution or something more complex.  Here are four commonly chosen options for greenhouse use, and some considerations to keep in mind. It’s important to note that they are not the only solutions, and that some farms may benefit from several different ways to treat their water in series because of their crops, setup or disease pressure.

Before getting started on an installation, there are many aspects to consider:   What is the size of your operation? Do you have any future plans for expansion? How do your production cycles work? Do you have heavy seasons, or fairly predictable week-to-week production? What’s your water source? Does your irrigation water come from a well, city or do you collect rainwater? Does the source change over the year? Do you blend water sources? What’s the water quality, and what is the volume you need to treat? Does it have sediment, or have you had disease issues? What types of crops do you grow? Sensitive varieties might require more vigorous treatment What’s your budget? What costs can you handle for up front installation and ongoing maintenance? How much maintenance can you handle? Is your ideal system a set-it-and-forget-it solution, or will it have downtime or need to be calibrated on a regular basis?

Ultraviolet Light (UV)

How it works: Damages DNA of pathogens and prevents reproduction by exposing them to UV radiation.

Type: Physical Capital Cost: High Operational Cost: Low Footprint: Small



• Requires clear and colourless water to work optimally, so water with high turbidity, sediment or colour will need a pre-treatment (like filters or a constructed wetland)
• Good choice for pathogen removal, especially in sensitive crops
• Good choice for growers managing high volumes of irrigation water
• Allows retention of nutrients if recirculating water
• Costly, especially if the volume of water warrants several units

Ozone

How it works: Splits ozone particles into oxygen and a free radical which destroys pathogen cell membranes.

Type: Chemical Capital Cost: High Operational Cost: Moderate Footprint: Moderate



• Like UV, water may pre-treatment to reduce turbidity, sediment, etc.. It can react with compounds in the water which can reduce efficiency.
• Removes fungi, bacteria and viruses, and breaks down organic chemicals such as pesticides or PGRs
• Controls biofilm if used properly
• Ozone itself is very unstable and must be generated on-site.
• Can add oxygen to the water which can improve root health
• Costly, especially if the volume of water warrants several units

Electro-Chemical Activation (ECA)

How it works: Passing a salt solution (generally potassium chloride, KCl) through an electrical current creates chlorine gas which dissolves into the water forming compounds which are antimicrobial.

Type: Chemical Capital Cost: Moderate Operational Cost: Moderate Footprint: Moderate



• Requires a product (KCl) to run which must be purchased to create your own treatment solution (low cost, but an ongoing one)
• Getting the right amount of active ingredient is a learning process, and it takes some optimization to get it right. Too much can result in phytotoxicity, too little doesn’t control pathogens. Regular water tests can help to see if it is working properly.
• Good pathogen control if monitored and maintained
• Controls biofilm if used properly
• May not be the best solution for chlorine-sensitive crops (buildup of ions (K and Cl) must be managed)
• Can be injected at multiple sites (e.g., at cloth filter before it goes into feedwater storage tanks, or as water goes out to crop)
• Moderately costly to install

Woodchip Bioreactors and Hybrid Treatment Systems (HTS)

How they work: The woodchip cell creates an environment with no free oxygen so beneficial microbes can degrade unwanted compounds (nitrate-nitrogen, and fungal pathogens). Additional compounds may also be removed, including pesticides and plant growth regulators.  In an HTS, the woodchip cell is followed by mineral media cells to remove other compounds such as phosphorus.  Media can be specific to meet the growing operations’ requirements.

Woodchip Cell Alone: Type: Biological Capital Cost: Low Operational Cost: Low Footprint: Moderate

Hybrid Treatment System: Type: Biological/Chemical/Physical Capital Cost: High Operational Cost: Low Footprint: High



• Can remove nutrients and fungal pathogens from water, as well as some pesticides and PGRs
• Water quality is suitable for irrigation but can have high bicarbonates and should be blended with fresh nutrient solution if used on sensitive crops.
• Can handle seasonal water fluctuations.
• Maintenance is fairly simple. Woodchips will need to be replaced as they degrade, but they have a lifespan of many years if the system is operated properly.
• HTS needs space for an in-ground system outside of the greenhouse, but can be installed under a growing area (machine traffic should be avoided)

For more information, check out these factsheets on hybrid treatment systems and biofilters. An article on using membrane filters, heat pasteurization and other filtration/treatment techniques by our colleague Dr. Fadi Al-Daoud can be found here.