Fast growth and rising productivity in the last decade lead to an increase in the cities and conurbations.
Additionally to the advantages of live in such a community, there are a number of problems involved with it. One of this is the lasting interference of the natural water balance, which is caused by the derivations of rainwater from the streets, ceilings and parking areas in the local canalization.
Thankfully, in the ´80 s there had been a change of view in the waste water management.
Concern the dealing with the flowing water of sealed surfaces.
In view of the perceptible negative ecological and economical effects of the conventional principle of the derivation in the canalization, they recognized the necessity of waste water drainage.
Even the legislator had recognized it (compare ATV 1999b). Furthermore the water guidelines of the European parliament and council (Guideline 2006/60/EG from 12.12.2006) had been come into force in the beginning of 2007. In this, measures are required which lead to a good chemical and quantitatively condition of the ground water and to guarantee this permanently.
This concerning a legal regulation will be expected also in Germany, as which it could be found already in certain regions. So, that a decentralized installation of a retention system is already required in many new building areas.
Also from the ecological site is a decentralized retention system practical. Initially it seems that it would be much easier to divert the rainwater to the existing canalization instead of the installation of a retention system, but the layerperson doesn’t see the costs depending on this.
On this way the pipe diameter of the canal system for the discharged water quantity has to be oversized
Rainwater collecting tanks have to be of an appropriate size to prevent a flooding even by
a big rain occurrence.
So the polluted rainwater with waste water has to be costly cleaned in waste water treatment plants.
The costs created by this way will be turned on the consumer by the cities and countries. There could be a plus of 500 € costs in a year for a one family house.
In connection with rainwater utilization system, with which we could save water costs and often state-subsidized, the incurred costs will be covered relatively fast. Considering the always increase rates for sewage disposal, such a system will develop his saving potential very fast. Different to the solar systems, were the amortization and changing time is closed together, the estimated durability of a retention system and rainwater utilization system is beyond 50 years and consequently to see it as an investment in the future.