Water makes things clean, right? Whether you have clean water to start with, though, is uncertain. It may contain particulate matter, pathogens, excessive minerals or chemicals. This is particularly noteworthy when it comes to hydroponic systems. For growers, the quality of your water is of paramount importance. “Poor quality water can cause toxicity problems, disease, pH problems and the blockage of drippers and plumbing.” (Flairform) Managing water quality is not a simple task. As the authors of Water Treatment for Pathogens & Algae (Fisher) observe, “Water treatment for horticulture involves perspectives from water chemistry more common to the swimming pool and municipal treatment industries than horticulture, in addition to plant pathology, engineering, and financial analysis.”
My goal in this month’s blog is to break down this very complex topic into smaller components and, as always, to provide resources from the experts to give you the tools you need to keep your water clean and your plants happy.
KNOW YOUR WATER
When growing hydroponically, it’s a given that you will need to invest in some form of water treatment. In order to determine what treatment is necessary, you have to know your water. The first step is to consider the source. Where it comes from will determine what issues you may have to address. Here are the traditional sources of irrigation water:
- Rain Water
Municipal water tends to be the cleanest, both in terms of pathogens and particulate matter. It may contain substances such as flouride that you don’t want. Hard water may have a high pH or contain an excessive level of minerals. Water from ponds and other catchment systems are the most likely to contain unwanted organic matter.
The second step is to have your water tested for pH, EC, Total Dissolved Solids (TDS), alkalinity and pathogens. Knowing what nutrients your water contains will allow you to choose a fertilizer that balances the nutrients in the water with what your plants need. If your water is very alkaline, that could impact the pH of your growing medium. Growing systems of any kind are extremely dynamic!
KNOW YOUR SOURCES OF CONTAMINATION
Knowing the quality of your water when it enters the building is not enough. You also need to understand where the sources of contamination are in your growing facility. Pathogens, for example, can be transferred from many surfaces.
Potential sources of pathogens in the greenhouse are:
- Water source
- Water holding tanks
- Biofilm from irrigation pipes
- Growing media
- Greenhouse surfaces
In recirculating systems, particulate matter can come from the crop and your growing media. If your fertilizer is high in salts, those salts will accumulate in the water. A clean growing facility is just as important to water quality as water treatment is.
DECIDE ON BEST TREATMENT FOR YOUR SITUATION
It’s important to note here that water sanitation and water sterilization are not the same thing. You want to sterilize your system between plantings to remove all harmful pathogens. Water, however, is a living thing. “… many of the microorganisms present in biofilm, soil, and water have been shown to have a benign or beneficial role, and plants may be more susceptible to pathogens when these organisms are eliminated.” (Fisher) So, the goal of water treatment is to sanitize your water, not sterilize it.
Treatments for pathogen and algae removal such as ultraviolet light and chlorination work most effectively on water that is free from particulates. Depending on the type of water supply, you may need to install a filtration system to filter out particulate matter (ponds) or things such as excess chlorine or flouride (municipal). Filtration is essential for recirculating systems.
To optimize treatments such as chlorination and copper ionization, you will need to take into consideration the pH and the amount of soluble salts. A low pH and/or a high level of soluble salts will render chlorination less effective unless additional chlorine is added. The efficacy of a copper ionization treatment is also dependent on soluble salts content. There’s a lot of chemistry going on here, folks!
METHODS FOR TREATING PATHOGENS AND ALGAE
Choosing the system that is right for your growing operation is dependent on the size of your operation, how much you can afford to spend and what water quality issues you have. Water that comes from holding ponds and other water catchment systems is likely to contain harmful pathogens. There are a number of treatment options for this which include:
- Sodium and calcium hypochlorite for chlorination
- Gas chlorination
- Chlorine dioxide
- Activated peracids
- Copper ionization
- Ultraviolet light
For descriptions of each and their relationship with pH, see Water Treatment for Pathogens & Algae
Food safety is on everyone’s minds these days and we are all responsible for making sure that the products that leave our facilities are safe. To that end, you should regularly test your water for pathogens to make sure your treatment method is effective. Be sure to test from the highest risk locations in your irrigation system such as where water is discharged from pumps or at the point where it has been in the system the longest. Testing labs should be accredited to ISO 17025 standards.
METHODS FOR TREATING HIGH SODIUM LEVELS
Sodium is a nutrient that is present in some water to a degree that is toxic to plants. Additionally, because salts are not taken up by plants in any great amount, they will accumulate in the water in recirculating systems. There are several ways to avoid toxic build-ups of sodium. One is to treat your water with a reverse osmosis purifier. Another is to avoid fertilizers that are high in salts. Finally, you can cut your water with rainwater which is typically lower in salts.
When it comes to hydroponics, the quality of water used to irrigate crops is a key component of successful production. The initial quality of your water is determined by the source. The quality of the water your plants receive is determined by you. Get your water tested. Municipal water districts can send you a report or you can engage the services of a water quality testing lab. Then seek out the services of a reputable company to determine what treatment options will work best for you and your crops.
Water Sanitation Part 1: Biology of Pathogens in Water Sources
Water Sanitation Part 2: Pre-Treating Water Before Sanitation
Water Sanitation Part 3a: Oxidizers Used for Water Sanitation
Water Types, Quality & Treatments
Three Keys to Water Treatment Design