The quality of your water source is important, high amounts of chlorine or chloramines, like those found in tap or well water, can be very harmful to your fish and plants. You'll want to test for water hardness, which refers to the amount of calcium and magnesium found in the water. This can range from soft (0-75ppm) to very hard (>300pm). For healthy and happy fish and plants, your water should be fairly soft, between 50 and 100 ppm. Your water's pH is extremely critical, as it directly affects the nutrient levels in your system. Fish and plants prefer a pH around 6.8 to 7.0, and any drastic changes can have big consequences. You'll start a strong base of nitrifying bacteria that's able to transform your fish's waste into more suitable plant food through a process called cycling when first setting up your system. A particularly acidic or alkaline water source may complicate this process.
Rainwater typically has a neutral pH, and low concentrations of hardness. This water source is also almost completely free of salinity, which is good, as longterm inputs of highly saline water can lead to build-ups of salt within your system. Rainwater is often a great choice for aquaponics system, however, in systems affected by high levels of pollution, acidic rain may be a concern. Wellwater can vary greatly in it's quality. Limestone bedrock will lead to fairly high levels of hardness within the groundwater, which can similarly heighten the pH. Surface water, like rivers, streams, or lakes, are typically more contaminated than other sources. These are open to runoff and pollutants, and can come full of nutrients of their own. Tap water, or municipal water, is often treated with pathogen-preventing chemicals, like chlorine. These will hurt fish and bacteria alike, so it's likely necessary to dechlorinate your tapwater before adding it to your system.
