Water is the lifeblood of agriculture. Not only does water irrigate roots, but it also delivers oxygen and essential nutrients to plants for healthy growth, big yields and high crop quality.
The quality of irrigation water is paramount. Poor water quality can lead to problems like stunted growth, nutrient toxicities or deficiencies, accumulation of harmful heavy metals in plant tissue, and bacterial contamination; in severe cases, it can even lead to plant death.
Assessing water quality involves more than just its appearance, as water can dissolve harmful impurities that are invisible to the naked eye. A variety of factors affect water quality.
In this blog post, we’ll discuss what those factors are and how they can help you determine if your water source is suitable for use in cultivating high-value crops.
Factors that affect water quality
Hydroponic growers should test their water across all of the following dimensions before using it in their grow operations to ensure it is suitable for both plants and irrigation equipment.
Electrical conductivity
Electrical conductivity (EC) measures the water’s ability to conduct an electrical current. Since salts carry a charge, EC determines the water’s salt concentration. The higher the EC, the more salts there are. Take, for example, that most well-known salt: sodium chloride (NaCl). Too much NaCl can cause water stress, when the plant can’t absorb water, causing wilting. Salinity stress occurs when one or more specific elements accumulate to the point of toxicity. It can also result in nutrient antagonism, which is when the presence of a nutrient limits the availability of one or more other nutrients. For instance, too much sodium can prevent the absorption of calcium.[1]
A study on the effect of salinity on hydroponically grown lettuce found that when salinity levels were above 2.0 decisiemens per meter (dS m-1), fresh yield was reduced, while salinity above 2.6 dS m-1 reduced plant growth.[2]
Total dissolved solids
Water with high EC levels should also be tested for total dissolved solids (TDS), as a high concentration of ions leads to higher TDS. TDS measures the total material dissolved in water, including sulfates, bicarbonates, sodium, carbonates, calcium and magnesium. Not only do high TDS concentrations influence water salinity, but they also reduce water clarity and can clog irrigation emitters.
Total suspended solids
Total suspended solids (TSS) concentrations above 50 milligrams per liter can cause emitter clogging in drip systems. Fortunately, effective filtration can prevent clogging by disintegrating suspended matter for easier flushing.
Turbidity
Both TDS and TSS contribute to water turbidity, which is a measurement of water clarity. High turbidity levels indicate cloudy water, which can lead to clogs.
pH
Nutrient solubility depends on the solution’s pH. If the pH is not within the optimal range, certain nutrients may become less or completely unavailable, resulting in nutrient deficiencies.
Since pH also indicates the concentration of hydroxyl ions and hydrogen ions in the water, it impacts the ability for flocculation and coagulation,[3] which can lead to emitter clogging.
The ideal pH for the nutrient solution in hydroponics is 5.8–6.3. Products such as Emerald Harvest’s PH Up and Down can help balance pH.
Alkalinity
Alkalinity measures the water’s ability to resist changes in pH. The higher the alkalinity, the more difficult it is to raise or lower the pH.
It can be measured by adding up the sum of carbonic acid, bicarbonates and carbonates in the water.
Water soluble salts
Growers should test the levels of nutrients and other elements in the water. While some nutrients like potassium, calcium and magnesium are beneficial, others, including sodium and carbonate, can be harmful; even high levels of bicarbonate can be detrimental, either as a plant toxin or by interfering with the uptake of other essential nutrients.[4] Boron is another nutrient to watch out for. Although it is a micronutrient, high concentrations can cause toxicity, and it can be present in irrigation water as un-ionized boric acid.
Figure 1 shows the EC and different compounds and elements that may be found in irrigation water and their limitations in hydroponics.
Figure 1. EC and compounds and elements found in irrigation water. Source: See footnote 1.
Heavy metals
The presence of any toxic heavy metal makes water unsuitable for irrigation.
Sodium adsorption ratio
The sodium adsorption ratio (SAR) is the relative proportion of sodium to calcium and magnesium ions. High SAR levels can cause scaling, corrosion and clogging in irrigation systems.[5] Growers should avoid using water with a SAR value greater than 10 millimoles per liter.
Temperature
Water temperature affects oxygen levels, with cooler water holding more oxygen. Water should consistently be around 65–75°F to ensure adequate oxygen levels for plant metabolic activity.
Water temperature can also damage irrigation equipment if the water pH is high. Magnesium and calcium carbonate solubility is inversely proportional to temperature. When water exceeds 64°F (18°C) and the pH is 7.2 or more, these carbonates precipitate in the lateral tubes and drippers, coating the irrigation equipment. The precipitation process is irreversible.
Bacteria
Bacteria present in the water can form biofilms—microbial colonies that attach to hard surfaces or clump together and create clogs. Biofilms can also deoxygenize water and carry harmful pathogens that infect plants.
Hardness
Hard water forms scales in irrigation pipes, heating elements and pumps, which can cause blockages.
Monitor water quality and equipment
Even after a water source is determined safe for use in hydroponic cultivation, it is important to check the following regularly:
- pH determines both nutrient solubility and availability. The ideal pH for hydroponic nutrient solutions is 5.8–6.3. However, growers can aim for 5.5–6.5.
- EC and TDS indicate nutrient concentrations in the solution. If they are too high, they may cause nutrient burn, while low measurements may indicate nutrient deficiencies.
- Dissolved oxygen (DO) is crucial for healthy root growth and nutrient uptake. Using advanced tools like DO and oxidation-reduction-potential sensors can be helpful.
- Alkalinity can be neutralized by supplementing the nutrient solution with acids.
In addition to testing the water, inspect and perform preventive maintenance of irrigation equipment frequently. Regularly flush tubes and pipes to remove unwanted debris and expand the lifespan of emitters by up to 35%.[6] Consider using water treatment methods like carbon filtration to reduce contaminants like chlorine, chloramine, sodium and bicarbonate.
Using high-quality water is crucial for hydroponic success. By testing your water irrigation source prior to cultivation and frequently monitoring its quality throughout the crop life cycle, commercial growers can ensure healthy, high-yielding, high-quality crops.
Emerald Harvest Team
[1] Van Os, Erik, Chris Blok, Wim Voogt, and Laith Waked. 2016. “Water quality and salinity aspects in hydroponic cultivation.” https://edepot.wur.nl/403810.
[2] Andriolo, Jerônimo L., Gean L. da Luz, Maiquel H. Witter, Rodrigo dos S. Godoi, Gisele T. Barros, and Orcial C. Bortolotto. 2005. “Growth and yield of lettuce plants under salinity.” Horticultura Brasileira 23 (4): 931–934. https://doi.org/10.1590/S0102-05362005000400014.
[3] Flocculation is agitating the water to encourage the development of “flocs,” a loose clump of fine particles that will settle in the water, while coagulation creates flocs through a chemical reaction. Source: Florida A&M University-Florida State University College of Engineering. N.d. “Coagulation, flocculation and clarification.” Accessed August 30, 2024. https://web1.eng.famu.fsu.edu/me/senior_design/2016/team09/lit9.pdf
[4] See footnote 1.
[5] Anyango, Geophry Wasonga, Gourav Dhar Bhowmick, and Niharika Sahoo Bhattacharya. 2024. “A critical review of irrigation water quality index and water quality management practices in micro-irrigation for efficient policy making.” Desalination and Water Treatment 318. https://doi.org/10.1016/j.dwt.2024.100304.
[6] Ibid.
