Nature has adapted to pollution and stresses in the environment which have influenced the evolution of the natural water purification process. Both natural and man-made impacts can affect water quality. In order to survive, mechanisms for cleaning water are necessary to remove impurities and make the water safe for all organisms. According to the U. S. Geological Survey, about 63 percent of the public water supply comes from surface water sources like lakes and streams. Natural water purification, therefore, has a direct impact on humans.
Wetlands act as nature's water filters. The Ecological Society of America estimates that they can remove up to 60 percent of the metals in water and up to 90 percent of the sediment from urban and agricultural runoff. Metals such as mercury and lead can have serious human health effects; their removal is imperative to good water quality. Removal of sediment helps prevent sedimentation in lakes and streams. It will also help prevent cloudiness which can negatively affect micro-organisms and aquatic plant life.
Wetlands naturally filter water by slowing its flow. Suspended particles, metals and other impurities drop into the sediment layer of wetlands. Over time, they become sequestered from the environment as additional layers of sediment cover them. Bacteria in plants and within wetland soils decompose organic matter, which can cause gastrointestinal illness, explains the U.S. Environmental Protection Agency.
Soils, particularly well-draining sandy soils, also filter water naturally, trapping particles as water percolates down through the soil layers. Filtration mechanically removes large pieces of debris. Bacteria and soil micro-organisms further purify water naturally by breaking down nutrients and contaminants.
Several environmental issues threaten the ability of natural water purification process in nature. Wetlands are particularly vulnerable. The U. S. Geological Survey estimates that over 50 percent of the U.S. wetlands in the lower 48 states have been wiped out since European settlement in the 1780s. The loss of wetlands removes an important source of flood and erosion control. Agricultural and urban runoff dumps contaminants such as pesticides, fertilizers and petroleum products onto soils and into lakes and streams.
In order for natural water purification to continue, protection and restoration of wetlands is essential. You can begin in your own yard. Construction of rain gardens can replicate the effects of wetlands. A rain garden is a depression in the land where water can collect. Planting wetland plants at the site will allow the filtration process to continue. You can also protect shorelines on your property by planting vegetative filter strips to prevent soil erosion and runoff, recommends the University of Minnesota Extension.