This article addresses the quality standards required for water for hydroponic production. Any hydroponic system will require sizable amounts of good quality water as the basis for the nutrient solution. However, the best water supplies contain substances and elements that might influence plant growth, either positively or negatively. It is, therefore, no surprise that even collected rainwater might contain organic and inorganic substances and elements.
The water from the water source must adhere to specific requirements before infusion with all the appropriate nutrients required for all stages of crop development. That will ensure optimal root and plant growth and deliver an exceptional yield. For this reason, every producer needs to understand the requirements of the water used for the solution.
Hydroponic crop production is an intensive endeavor, and the manipulation of the solution will make the difference between an exceptional yield or a poor yield. However, in this article, we will supply you with background knowledge enabling the producer to understand the water requirements used as the basis for the solution. Furthermore, this article will enable you to manage the raw water yourself by further studying the topic. Finally, the knowledge gained will allow you to ask appropriate questions when a third party is enrolled to work on the solution.
The water source you will use needs to supply a constant amount of water to keep your hydroponic project going and the crops well-watered. Therefore, a sustainable water supply is needed as water shortages can reduce yield, and crops might die if a prolonged water deficit occurs.
The amount of water needed for hydroponic production will depend on your hydroponic system, storage available, etc. As a general rule of thumb for hydroponic production, small plants will use a ½ gallon of water per plant, while medium plants will require 1 ½ gallon and large plants 2 ½ gallons of water per day.
Using storage tanks for raw or pure water as well as your infused solution can neutralize water shortages in the case of emergencies and is a valuable part of a hydroponic system. Calculators are available to estimate the size of storage units and can be calculated by greenhouse suppliers found on Google as well.
At this stage, we know that the solution is the main component that drives exceptional high yields in a hydroponic system. However, it is necessary to ensure that the water from your source can accommodate the goals you want to reach with a nutrient infusion. Specific characteristics of the water may interfere with nutrient availability and nutrient uptake by the plant, adversely affecting growth and yield.
If a reverse osmosis system is present, testing the water will give insurance that the water is inert, without any minerals. It will, however, be advantageous to measure the pH and EC continuously to address problems as they arise.
Therefore, it is imperative to send the water you will use as the basis for your solution for laboratory analysis to alleviate possible problems that might lead to malnutrition and thus a waste of nutrients and money spent on the ingredients of the infusion. In addition, because water from your source may vary over time, regular water testing will be needed to ascertain the quality of the water you use in a hydroponic system.
Before taking the water sample, contact the lab that will conduct the test to ascertain their criteria. They will probably supply you with a test kit that might include instructions.
The following characteristics of your water source determine the quality of the pure water for use in a hydroponic system. Wherever abnormalities occur, producers can address these problems through filtering and additions.
These factors include physical, chemical, and biological factors. Physical properties include suspended particles in water, and they substitute a clogging hazard for pumps, sprayers, and drippers in hydroponic systems. Biological properties include the presence of Iron fixing bacteria, plant pathogens, and algae. Iron fixing bacteria can grow in water generating excessive iron concentrations that limit plant growth. The excessive Iron can clog sprayers and contribute to excessive rust of all metal parts of the system. In addition, algae might be present in slow-moving water or ponds. Therefore, it would be beneficial to specifically ask for an appropriate test because it is not usually part of a standard water quality test. Water tests are primarily aimed at Chemical properties because they can negatively influence plant growth, nutrient availability, and the plant’s ability to utilize nutrients dissolved in the water.
The pH of water indicates the acidity of the water and measures the concentration of hydrogen ions (H+) in the water. For example, water with a pH measurement of 7 is neutral, whereas a pH above 7 is alkaline (not the same as Alkalinity), while a pH below 7 is acidic. Most crops grow well with a pH between 6.0 and 7.0, but it is essential to note that every crop has different pH requirements that must be met to obtain the maximum response to nutrients that increase yield and thus ROI. On the other hand, the availability of nutrients is influenced by pH, as indicated by the following diagram:
Producers must determine the pH of raw water before infusion with nutrients because the kind of fertilizer you use will affect pH; therefore, you might set minor pH deficiencies right by selecting the correct type of fertilizer. In other cases, specific additives might solve an incorrect pH.
Alkalinity measures the water’s ability to neutralize acids and includes acids found in fertilizers. If the alkalinity of water is high, it will neutralize acids and may become more alkaline over time. There is a direct correlation between pH and alkalinity that influences the effect of different chemicals to increase and decrease water pH.
Laboratories report Alkalinity in meq/L (milliequivalents per liter) or ml/L (milliliter of calcium carbonate per liter of water). The substrate is usually inert in hydroponic production and does not buffer the water. In contrast, the amount of water present in a hydroponic system is limited, and problems can occur with an Alkalinity as low as 0,75 to 1.25 meq/L for small volumes of water.
The electrical conductivity is a measurement of the total dissolved salts (Free ions) in the water. The conduction of electric current through the water is accommodated by the free ions present in the water, giving the EC of the water. Pure distilled water will not conduct electricity because it contains no ions, and the EC will be zero.
Electrical conductivity is measured in mmho/s, the reciprocal of ohm, a unit of electrical resistance, and the scientific standard for measuring EC. Water for hydroponic systems, with an EC close to 0, is preferred as ions (nutrients) will be added during the water infusion with nutrients. Therefore, a lower EC will make nutrient management easier than a higher EC. On the other hand, an excessive EC can lead to toxicity and retarded plant growth.
Macronutrients can be present in raw water and should be taken into consideration when planning the nutrient infusion. This practice can cut costs on nutrients and is necessary.
Nitrogen (N), Potassium (P), Potassium (K), Calcium (Ca), Magnesium, and Sulphur (S) in raw water can be utilized by the plant if moderate amounts are available. However, the availability of Nitrogen and Potassium in substantial amounts might not be harmful. Still, it might indicate a contaminated water source, and you should do additional tests to determine the precedence of contaminants, as they can induce adverse effects.
The relative concentration of some of these elements can indicate other problems, such as the “hardness” of the water. Hardness is a measure of dissolved nutrients, usually a specific form of Calcium and Magnesium ions in the water. For example, when too much Calcium and Magnesium chloride is in the water, it can cause the “hardness” of the water. Take note that this will not influence the Alkalinity of the water.
Zink (Zn), Copper (CU), Iron (FE), Manganese (Mg) and Boron (B), and Fluor (F) might be present in the water at varying levels, and sometimes their levels can be excessive. Micronutrient toxicity is more prevalent at low pH values because more micronutrients are available to the plant.
Plants need micronutrients in minute quantities, but deficiencies will lead to plant damage and reduced yield, while too much may be toxic. Therefore, micronutrients should be considered before the nutrient infusion to maximize the growth and yield of the crop planted.
When utilizing tap water, remember that Fluoride is an added constituent to tap water, and too much F in the water might cause fluor toxicity to plants. Therefore, always verify the F toxicity levels of especially city water for each planted crop to eliminate fluor toxicity.
People or companies specializing in that discipline can interpret results accurately, like local co-ops. In addition, some of the suppliers of substrates, greenhouses, and even independent companies, as well as educational institutions like Texas A&M University, can aid you with the accurate interpretation of the results.
But suppose you can understand and grasp the complex chemical components in the water test environment. In that case, you are much better qualified to manage all aspects of water and solution management in your soilless production yourself. Therefore, we will discuss the basic parameters available in a water test, considering each parameter’s target range and acceptable range.
The target range and acceptable range of nutrients and other components in raw water for hydroponic production were derived from research and can be compared to the figures obtained from a water test.
| Component | Target Range | Acceptable Range |
|---|---|---|
| pH | 5.5 – 7.0 | 4 – 10 |
| EC | 0.2 – 0.8 mS | 0 – 1.5 mS |
| Sodium (Na) | 0 – 20 | < 50 |
| Chloride (Cl) | 0 – 20 | < 140 |
| Alkalinity x | 40 – 160 | 0 – 400 |
| Ammonia (N) | Na. | < 10 |
| Nitrate (N) y | Na | < 140 |
| Phosphate (P) | O – 3 | < 5.0 z |
| Potassium (K) | Na. | < 100 |
| m (Mg) | Magnesiu10 -30 | < 50 |
| Calcium (Ca) | 25 – 75 | < 150 |
| Sulphate (S) | 0 -40 | < 100 |
| Manganese (Mg) | < 1.0 | < 2.0 |
| Iron (Fe) | < 1 | < 4 |
| Boron (B) | < 0.1 | < 0.5 |
| Copper (Cu) | < 0.1 | < 0.2 |
| Zinc (Zn) | < 0.5 | < 0.3 |
| Fluoride (Fl) | < 0.1 | < 1.0 |
| Molybdenum (Mo) | < 0.1 | < 1.0 |
Al units are expressed in parts per million (ppm) except were stated differently.
A more in-depth discussion of the complex interactions between these elements that influence parameters like alkalinity and salinity can be found in various other publications that we recommend you to read to understand the interactions better.
A periodic water test is needed because water quality can change due to various factors. On the other hand, producers should measure pH and EC continuously to eliminate damage to the crop due to fluctuations. In addition, slight changes might influence nutrient uptake and growth negatively.
On the other hand, you can negate all this effort by installing a reverse osmosis plant to ensure that you utilize inert water without all the complex interactions found in normal water. You can then supply all nutrients to meet crop needs. You might have to compensate for their EC value with specific substrates if needed.
However, after testing, evaluating, and correcting major issues in the raw water, you can infuse your water accurately with adequate nutrients, take the EC if any of the substrates into consideration, and start planting. We will discuss the selection of the best substrate for your cropping system in the following article.