An activity or production process can be said to be sustainable if there is no impact on the environment and renewable raw materials are used.

Natural environment
Water is a product that is borrowed from the cycle. The cycle must be undisturbed as far as possible. Human interference must be restricted. Where water is needed it will have to be abstracted from the cycle at a suitable place so that the natural environment is not damaged. For all production processes the consumption of water must be curbed. After the water has been used, it is returned to the cycle with the same quality as before. Borrowing water from the great cycle is the correct expression. Taking in upstream and returning unchanged downstream is the correct approach.

Example
Water has something pure and natural about it. A waterworks has an exemplary function to fulfil in today’s society. Within the WMD this led to the viewpoint that, for the construction of the large new Annen treatment plant, sustainability had to be the guiding force. Annen treatment plant is an example of maximum sustainable production and transport of drinking water.