The sludge is often spread over soil and can find its way into the groundwater. Urban runoff from roads, parking lots and storm sewers can also contribute to water pollution as it picks up chemicals, soil, trash and oil products. Municipalities also use pesticides and herbicides in parks, golf courses and along roads to control pests and weeds. These chemicals also find their way to the groundwater. Finally, commercial activities in cities and towns contribute to water quality problems.
Many businesses use chemicals as sales products, in processing and as cleaning agents.
One particularly important problem is storage tanks, either above or below the ground, which can leak chemicals into the groundwater. A final source of water pollution is individuals. Within the home a number of toxic chemicals are used for cleaning, painting and car care. Often people do not consider the potential damage to ground and surface water when they dispose of these chemicals in the sink, toilet or trash. About 25 percent of all homes use septic systems for sewage disposal.