- some streams consist only of sewage-surface water supplies require expensive treatment. In terms of numbers of systems supplying water, wells are the most common and to date, very few water supplies from wells need treatment to make the water safe to drink. Prevention of contamination is much less expensive than paying to remove contaminants, particularly when treatment must be done by the homeowner instead of the community as a whole. For many years, it was assumed that connection to public sewers should be the goal of every household. Only recently have the fed- eral government and a few engineers, city councils, and county commissioners come to the realization that in many areas, onsite disposal is far more cost-effective than a collection system and a central treatment unit. Many of the sophisticated treatment plants built in rural communities have posed significant problems to those communities that could not afford the maintenance costs, paying skilled operators to manage the facilities, or paying the pollution fines resulting from improperly operated facilities. Onsite disposal is a viable alternative to sewerage. It often pro- vides a greater degree of protection to public and environmental health than a public facility, and at far less expense to the home- owner and the taxpayer. Given the fact that nonmetropolitan areas have been growing faster than cities, the future will bring an increasing concern for the health and environmental effects of on- INTRODUCTION 3 site sewage disposal, as well as an increasing emphasis on the proper design, installation, operation, and maintenance of these on- site systems. Onsite disposal systems can provide adequate ground and surface water protection for present and future generations, or they can make water totally unfit for consumption. Proper design, location, installation, and maintenance make the difference between these two scenarios. The one-half million new onsite systems being built each year have significant potential to impact ground water quality over lar