Water used to fill ponds must be of high quality and free of pollutants such as sewage and toxic chemicals. Water that is suitable for livestock and home use or that supports wild fish populations is generally safe and suitable for use in farm ponds. Fish grow best in water with certain chemical characteristics. Ideally, water should have a pH of 6.5 - 9.0, total hardness of 50 - 300 mg/l and total alkalinity of 50 - 300 mg/l. Total hardness and alkalinity should not be less than 20 mg/l. Most freshwater sources across North America will meet these criteria and be suitable for fish. Simple water tests can determine whether or not your water meets these basic guidelines. Other important factors include maintaining suitable oxygen levels and controlling turbidity (muddy water or phytoplankton).
Most ponds in the U.S. are watershed ponds that depend totally on rainfall runoff across pastures or woodlands to fill and maintain water levels, so water quality is affected by the type and soil composition of the watersheds. Waters of low alkalinity usually originate from acid soils, whereas waters with higher alkalinities drain across soils with sufficient quantities of limestone.
Watersheds must be well vegetated to keep pond water from becoming turbid with mud. Runoff from cropland is not suitable source water for ponds because of potentially harmful pesticide contamination, fertilizer runoff and excessive turbidity. Pastures make good watersheds if not overcrowded with livestock. Too many animals on a pasture will result in excess nutrients entering the pond, causing serious problems with water quality.
Well-vegetated woodland watersheds are usually excellent sources for filling ponds. Runoff is typically clear and free of contaminants, but temporary problems with muddy water may occur after heavy logging activity. Water from pine forest watersheds is usually a bit acidic (low pH), and the addition of limestone may be required in some ponds receiving this water.
Canals, streams and rivers may also be used as sources for pond water if certain precautions are taken. Water from these sources is often used when ponds are built in areas with little or no natural watershed, such as in a level field. Many levee farm ponds are filled with water pumped from surface water sources. Surface water may be used if free of contaminants. Water must be carefully filtered with a fine mesh screen to minimize the possibility of stocking ponds with undesirable species of trash fish. Make sure the screen does not clog with debris while pumping, allowing unscreened water to enter the pond.
Groundwater sources such as water wells and natural springs usually provide excellent quality water for farm ponds. Water wells must be used when surface water sources are unacceptable or not available. Wells are expensive to install and operate and must be of sufficient size and capacity to be useful. An undersized well in an oversized pond may operate continuously and not even keep up with evaporation.
