In a highly developed country such as the Netherlands, the sewerage would seem to be complete: 98% of the homes are connected to the sewer system and 100% of the collected waste water is purified, and within a couple of years all purification will comply with the European norm for the removal of nitrogen and phosphate. This waste water system is perfectly capable of complying with its two essential social requirements, i.e. the advancement of national health and the reduction of environmental pollution. The current system is, however, not up to the challenge of the 21st century i.e. the reduction in the waste of raw materials, water and energy. Essential changes in the means of collection, transport and purification of waste water may be, therefore, expected. The social, ecological, water management and technological drives that lead to changes in the waste water system will be discussed below.