To sum up, the following may be said with regard to the environmental relevance of wastewater disposal projects:

The plants of such a project must be planned, built and operated in accordance with the generally accepted rules of the art or wastewater technology and, if hazardous substances are to be eliminated in treating wastewater, in accordance with the state of the art. One must take into account the immission situation (burden), other uses and the hydrological and biological capacity of the receiving body of water.

If the capacity of the receiving body of water in question is not sufficient to absorb the wastewater treated in accordance with the rules of the art, then for the sake of water quality, further requirements must be laid down for the treatment efficiency of the sewage works or the wastewater discharge. A management plan may then be necessary to ensure that the receiving body of water serves the good of the general public, in harmony with the benefit of individuals, and prevent any avoidable adverse effects (§ 1a WHG (11)).

As a general rule, every area must be appropriately treated before the drinking water can be used; this is especially true when wastewater discharges are situated above the point where water is drawn off.

As a general rule, to relieve pressure on wastewater disposal systems, the volume of wastewater should be minimised, both in the domestic and in the industrial and commercial sectors.

Other non-water related effects of a wastewater disposal project, such as occupation of land, noise and odour emissions, flue gas emissions etc. are normally of lesser importance in assessing the environmental relevance. This is because the plant components are mainly installed underground and because few installations affecting air purity, such as sludge incineration plants , are ever built.