Water and soil pollution can occur from both natural and human sources. Three major human-induced sources of water pollution are agriculture, municipalities, and industries. Pollutants can contaminate surface water through direct discharge or runoff, and groundwater by seeping into aquifers. Laws attempt to regulate water pollution but controlling nonpoint sources remains difficult. Soil pollution adversely impacts plant and animal health and often leads to water or air contamination. Remediation techniques can help clean contaminated water, soil, and groundwater.