The natural filtration of fish and plants will do a large part in keeping your water healthy; in aquaponics the water never needs to be changed, only topped off. While standard hydroponic systems need their water changed several times a year, aquaponics are a different kind of setup entirely. Instead of trying to simply grow plants in a relatively sterile environment, aquaponics farmers add fish to the equation and set up a symbiotic system that imitates a natural cycle. In this cycle, fish produce wastes like ammonium and nitrate, which can be directly absorbed by the plants as fertilizer. These substances, which could poison the fish if not removed regularly are managed entirely by the crops, rather than needing to be replenished with clean water. The constant availability of nutrients, on the other hand, allow those crops to grow rapidly, with little effort wasted on massive root systems that must search for water and nutrients.
This balance between fish and plants leads to high quality water, as long as everything is functioning in balance as it should. However, it's important to ensure the quality of your source water. Water from streams, local wells, or even natural springs can be contaminated with chemicals from runoff or seepage such as arsenic, pesticides, and other pollutants. It’s a good idea to test your well water for a broad spectrum of contaminants anyway, but especially if the fish and plants you're growing are for human consumption.
