We don’t water our plants with any ‘ole water. Learn about the water filtration techniques we employ for our plants, along with electric conductivity, water pH, alkalinity values, bicarbonates, and view lab test results!
Once we have our seed selections worked out we have to add the next crucial component of any crop – water! It’s not an exaggeration to say that water management is one of the most important parts in hydroponic cultivation. Understanding the water quality and how to manage it, is a crucial part of our overall cultivation process.
Water quality refers to the chemical, physical and biological characteristics of water. Depending on the purpose of the water usage, there are many different treatments and different standards of water quality evaluation. For hydroponic irrigation water, it is important to know the chemical characteristics as it greatly affects nutrient availability and plant health.
Water quality can be very different depending on the areas and water sources. Irrigation water can come from sources like a river, well, pond, rain water, and tap water, and each has its own chemical characteristics.
Our water quality process begins with municipal water from the tap as our source water. We then get testing performed both right from the tap, and after an extensive reverse osmosis (RO) filtering system. This way we know exactly what managing steps we must take to make our water perfect for fertigating our plants.
Many governmental and private laboratories conduct water quality analysis for different purposes, and one can simply send a water sample to the lab and pay to obtain the reports. The testing lab we currently use is JR Peters based in Pennsylvania. They provide great value in terms of cost, turn around, reporting, and services they offer. We’ve discovered they provide the best service we could find despite having local testing labs and having to ship out our samples to them on a regular basis.
Once the water quality pattern is established (we receive the lab results), we can begin to determine what will be needed to condition the water for cultivation purposes. For our irrigation water, we are concerned with the must-know water chemical characteristics:
1. Water Electric Conductivity (EC)
EC refers to the electrical conductivity of the water solution. When the water is pure without any dissolved solutes, it conducts electricity naturally. The amount of electricity that can pass through water is influenced by how many ions are dissolved in the water solution. By measuring EC, we can get an idea of how much ionic nutrients are in the water. For example, seawater’s conductivity is one million times higher than pure (deionized) water, because there are a lot of ions dissolved in the seawater, especially sodium (Na), chloride (Cl), magnesium (Mg), sulfate (S) and calcium (Ca).
The value of water EC can be obtained with an electrical conductivity (EC) meter. EC meters are relatively simple and stable, and can be purchased from most hydroponic shops. The higher the EC, the more solute salts and ions are in the water. Many horticultural guidelines provide the upper acceptable EC level for various plants depending on the species and growing stage. For example, the EC level for irrigation seedlings shouldn’t be higher than 0.75 dS/m, but for older crops in general, it can be up to 1.7 dS/m. For hydroponics, water EC provides an important indication of the amount of nutrients dissolved in the water solution.
In our process we measure the EC value of our source water to see the quality of the water, then after we run the water through a reverse osmosis unit which works on taking out dissolved salts in water.
In our case, the lab results (listed below) have our source water EC value at .77 dS/m before the reverse osmosis system, but afterwards we have a pretty clean value of .05 dS/m. The end goal is to take out as much of the salts out of the municipal water source then be able to add in exactly which macro and micro nutrients are needed for optimal plant growth. This process will be covered in a future nutrients blog post.
2. Water pH
pH = H+ and OH-
The pH is a measure of the concentration of the hydrogen protons (H+) and hydroxide (OH-) in a solution. If hydrogen protons predominate, the solution is acidic. If hydroxides predominate, the solution is basic. The pH is a numeric scale from 0-14 to determine the acidity and basicity of the water solution. The pH of pure water is neutral, pH=7. Solutions with pH less than 7 are acidic and solutions with pH more than 7 are basic. For example, the pH of lemon juice is around 2 and the pH of sea water is around 9. pH is measured in “logarithmic units”, meaning each number represents a 10-fold change in the acidity/basicness of the water. Water with a pH of 5 is ten times more acidic than water having a pH of 6.
The pH of the solution plays an important role for plant nutrient uptake. Water pH affects essential nutrients’ availability; in other words, when the water pH is out of range, plants cannot absorb nutrients even when there is plenty in the water. The desirable water pH for a hydroponic system is 5.6-6.2.
When the water pH is higher than 6.2, the availability of phosphorus (P), iron (Fe), manganese (Mn), boron (B), zinc (Zn), and copper (Cu) decrease. When the water pH is lower than 5.6, calcium (Ca) and magnesium (Mg) become unavailable. The pH of the nutrient solution has to be monitored constantly, as it only takes a short time for a pH that’s out of range to have a drastic impact on plant growth, especially for fast growing plants.
We use a variety of acids such as nitric acid, sulfuric acid, and phosphoric acid depending on the growth cycle of the plants to lower the PH of the feed water during the fertigation and carbonates and bicarbonates to raise the PH of the water.
Alkalinity refers to the capacity of water to neutralize acid, which is also commonly known as “buffering capacity”. This capacity is mainly influenced by how much carbonates and bicarbonates (H2CO3, HCO3, and CO3) are in the water solution. The main source of alkalinity in water is calcium carbonate (CaCO3), which are derived from carbonate rocks (limestone).
Water alkalinity has a significant effect on the pH of the water. If the water alkalinity is high, it is very difficult to adjust the water pH to the right range, because the buffering capacity of the water itself is very strong. In such conditions when alkalinity is high, growers will often have to inject a large amount of acid to bring down the water pH to the optimum range. Acids are usually in the form of a mineral such as phosphorus, nitrogen, sulphur, etc. this means more acid added to a fertigation solution can throw off a balanced nutrient profile given to the plants.
In truth, water pH, water alkalinity, and the pH of the growing mix are closely connected. Over time, all three factors affect fertility. For example, high or low soil pH values usually produce minor element deficiencies or toxicities. Of the two, water alkalinity is more important than water pH in influencing media pH. Water with high pH but low alkalinity will have little effect on media pH over time. However, highly alkaline irrigation water, regardless of its pH, may have a profound effect on media pH. Water pH is a poor indicator of the capacity of water to modify the pH of the growing mix; alkalinity, however, is an excellent indicator. Growers who intend to manage media pH must know the alkalinity of their water. Water pH can also affect the stability of some pesticides and growth regulators.
In sum, alkalinity is a measure of the water’s ability to neutralize acidity. An alkalinity test measures the level of bicarbonates, carbonates and hydroxides in water. The results are expressed as ppm of calcium carbonate (CaCo3). Levels between 20 and 55 ppm are considered optimum for most plants.
The lab results (listed below) have our source water alkalinity value at 241.64 ppm – this is not optimal! There is too high of a concentration of calcium carbonate (CaCO3) for any sort of container crop. However, after running the water through the reverse osmosis system we get a very agreeable value of 23.53 ppm – which is a great number to work off of to start building a nutrient fustigation program.
5. Specific elements
In some cases, too many specific elements may have a negative impact for plants; this is especially true for hydroponic cultivation. Despite these elements being essential for plant growth, plants only need them in such miniscule amounts that it’s very difficult for growers to adjust them during application. This is one of many reasons why we choose to use a reverse osmosis (RO) system to get rid of all the dissolved ions to start from scratch as much as possible. However, even with extreme filtering some specific elements such as Calcium (Ca), Nitrate (NO3), Ammonium (NH4), Magnesium (Mg), etc. are still present. We must take these trace amounts into consideration when building up our water quality and nutrient profile which is best suited for our plants to maintain optimum growth. This in turn leads to excellent cannabinoid and terpene content and profiles.
The following is a post of our lab results out of the tap and before the reverse osmosis system:
The lab results after the reverse osmosis system: