The best water for hydroponics has no contaminants, an EC close to 0 millisiemens and a pH of 7[1]—a level of purity that makes it easy to provide everything plants need without risk of toxicity.
Unfortunately, most water sources are not this pure. Some contain high concentrations of sodium or iron, which can be harmful to plants and are hard to manage in hydroponics. Water containing chloride can be especially challenging; issues can arise at just a few parts per million. Some water sources are more likely to harbor pathogens[2] and diseases,[3] while highly saline water can significantly reduce photosynthesis.[4]
Growers must be meticulous in selecting a water source and test its quality before using it in hydroponic production. We will discuss the most common water sources available for irrigation and their general qualities.
Common sources of water for hydroponics
- Tap water is a popular choice. It is readily available, filtered and chemically treated to remove impurities and bacteria. However, tap water may contain chemicals that alter its pH and harbor chlorine, chloramine or fluoride, which must be filtered out before use.
- Surface water (e.g., from lakes, rivers, etc.) is risky to use in hydroponic cultivation, as it is a common source of pathogens and can be contaminated by sewage, discharge from storm drains, animal feces or runoff from fields or industrial and municipal effluents.[5]
- Groundwater (e.g., from aquifers, wells, etc.), while generally safer than surface water, may still be contaminated by heavy rains or floods. Well water may have a high mineral content, which can result in nutrient toxicity. Groundwater from limestone-rich areas can significantly raise the pH of well water.
- Rainwater is considered the best water source for hydroponics thanks to Mother Nature’s filtration processes of evaporation, condensation and precipitation, which yields water that is free of impurities and ideal for plant growth.
Figure 1. Some water sources used for irrigation and their related contaminants. Image source: Malakar, Arindam, Daniel D. Snow, and Chittaranan Ray. 2019. “Irrigation Water Quality—A Contemporary Perspective.” Water 11 (7): 1482. https://doi.org.10.3390/w11071482.
Use treated water
As we discussed in our last blog post, it is important to test water before using it in hydroponics. If water tests high in sodium, chloride or iron—elements that are difficult to manage and potentially harmful to plants—growers need to treat it before using it:
- Distilled water is purified through evaporation and condensation, which removes chemicals, heavy metals, bacteria and waste, resulting in water with a neutral pH that is ideal for hydroponic systems. Growers can purchase distilled water or make their own with a water distiller.
- Reverse osmosis (RO) water is purified by removing particles and contaminants as small as 0.0009 microns, which eliminates pesticides, heavy metals and other toxins found in many water supplies. The result is a nearly pure water source that allows growers to apply nutrients without worrying about unwanted heavy metals and bacteria.
While other filtration methods, such as activated carbon filters and sediment filters, can remove water impurities, RO is our preferred option because it uses several filtration methods to progressively remove impurities of all sizes.
Opt for the cleanest source
Water quality directly affects plant health, so selecting the right water source is crucial to hydroponic success. Growers should aim to start with the purest water possible—one that has low mineral content, a neutral pH and minimal contaminants. This gives them precise control over the nutrient solution, reduces the risk of toxicities and diseases, and helps to ensure healthy and prolific plant growth.
Emerald Harvest Team
[1] In other words, a neutral pH having the same number of H+ and OH− ions, like pure water.
[2] Gallas-Lindemann, C., I. Sotiriadou, J. Plutzer, and P. Karanis. 2013. “Prevalence and distribution of Cryptosporidium and Giardia in wastewater and the surface, drinking and ground waters in the Lower Rhine, Germany.” Epidemiology & Infection 141 (1): 9-21. https://doi.org/10.1017/S0950268812002026.
[3] Alegbeleye, Oluwadara Oluwaseun, Ian Singleton, and Anderson S. Sant’Ana. 2018. “Sources and contamination routes of microbial pathogens to fresh produce during field cultivation: A review.” Food Microbiology 73: 117–208. https://doi.org/10.1016/j.fm.2018.01.003.
[4] Endalu Tara, Lelisa and Tasisa Temesgen Tolossa. 2020. “Systemic review: Effect of Irrigation Water Quality and Deficit Irrigation on Crop Yield and Water Use efficiency.” TURJAF 8 (5): 1201-1210. https://doi.org/10.24925/turjaf.v8i5.1201-1210.3366.
[5] Ibid.
