In 1973 the Montana passed the Montana Clean Water Act (CWA). The CWA called for a careful evaluation of all new and increased sources of pollution with the potential to enter state waters, both groundwater and surface water, and cause degradation. The Montana Department of Environmental Quality (MDEQ) began enforcing the CWA requirements in 1993. Specifically, the MDEQ Subdivisions Section began requiring that new subdivisions, and the development of existing parcels not previously approved by MDEQ, provide evidence that the installation of onsite wastewater systems (OWS) on those parcels would not cause degradation of state waters.

Much of the new subdivision in Montana is occuring outside of the boundaries of cities and towns. Most rural areas rely on individual groundwater wells for domestic water and OWS for wastewater treatment and disposal. The wastewater discharged by an OWS can cause degradation of both ground and surface water by elevating nitrogen levels, bacterial and viral counts and phosphorous levels. Because it was not practical to address all of these possible contaminants, MDEQ focused on nitrogen. Elevated levels of nitrogen as nitrates in drinking water are associated with "blue baby" syndrome or methemoglobenemia. Methemoglobenemia is a potentially fatal condition in which the hemoglobin in the blood of infants cannot transport oxygen through their bodies. The MDEQ defined the predicted concentration of nitrogen as nitrates in the groundwater after development to be an indicator of degradation.