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3.1 Water Sources

5 months ago

4 min read

Sourcing water is an important consideration, as it directly impacts system management and performance. Typically, 1-3% of total system water is replaced per day depending on climate, time of year, and crops being produced (Somerville et al. 2014). Water is lost in the system through evaporation, transpiration into the plant, and through normal processes of splashing, cleaning, and harvesting.

Water with a salinity above 0.8 parts per thousand (ppt) are typically not suitable for aquaponic production as the majority of cultured plants do not tolerate even a small degree of salt (Shannon and Grieve 1998). Common aquaponic crops with a salinity tolerance include lettuce (0.83 -- 2.8 ppt), kale (up to 7.4 ppt), Swiss chard (1.5 -- 3.5 ppt), and tomatoes (up to 5.8 ppt) (Maggio et al. 2007, Shannon and Grieve 1998, Shannon et al. 2000). Even though some crops do show an ability to tolerate salt, growth is compromised at some point during production..

The majority of aquaponic producers utilize rainwater, well water, municipal water or a combination for their systems.

Rainwater: Rainwater typically has a neutral or slightly acidic pH, slight calcium and magnesium hardness, and no salinity (Somerville et al. 2014). In large systems, rainwater is generally best utilized in conjunction with other sources to reduce overhead cost and improve sustainability.

Rainwater run-off can easily be captured from roofs or gutters and stored for later use. Water collected from roofs should be treated prior to use, as they may contain bacteria and pathogens from bird or rodent droppings. Considerations include areas that may receive acid rain, laws that prohibit collection, and roof material and age. Some research has suggested that new and aging roofs are not suitable for collection (Clark et al. 2008), as materials such as shingles, cedar, and uncoated galvanized aluminum can contaminate water with chemicals, heavy metals, and pollutants.

Well water: Well water is a viable option for some producers. Considerations include potential contaminants and bedrock composition. Chemicals that are particularly harmful include heavy metals, iron, and sulfur. Aquifers with bedrock composed of limestone have high water hardness and alkalinity concentrations. Alkalinity (bases in the water like carbonates, bicarbonates, and hydroxides) prevents swings in pH, which is naturally lowered in aquaponics from nitrification. Alternately, producers with very low fish production may require water treatment to decrease hardness and/or alkalinity before use (Somerville et al. 2014). Lack of fish and subsequent feed input can cause pH to remain too high, making certain nutrients inaccessible to the plant. Pumping rate of the aquifer will also need to be determined if it will be the only source of water for an aquaponic system. This is particularly important in systems that will require large water additions or replacement.

Municipal water: Municipal water is ideal for use in aquaponic systems. Chlorine in tap water eliminates bacteria, pathogens, and algae, making it a safe and reliable source of water. Chlorine and chloramines, however, must be removed before use as it is toxic to fish and will kill off the nitrifying bacteria.

Chloramine is basically a very stable molecule of chlorine bound to ammonia. Unlike chlorine alone, chloramines cannot evaporate out of the water. This provides rural households with a safe supply of drinking water but makes its use tricky for aquaponic producers. Free chlorine in the water can be gassed off in 48-72 hours with aeration. Chloramines require chemical dissipation (ex. sodium thiosulfate) or charcoal filtration. Given the small volume of water exchange, chloramines typically do not negatively impact an aquaponic system. Typically, you can replace around 10% of the system water volume without treating or testing for chlorine/chloramines.

Surface water: Surface water includes ponds, lakes, rivers, and streams. Surface water can introduce pathogens, algae, snails, and other organisms. In addition, many surface waters are contaminated with pollutants or agricultural run-off that pose a food safety threat to the organisms in the system and to consumers.

Source: Janelle Hager, Leigh Ann Bright, Josh Dusci, James Tidwell. 2021. Kentucky State University. Aquaponics Production Manual: A Practical Handbook for Growers.

Kentucky State University

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