1. General principles of sanitation

Historically, water drainage in urbanized areas was based on the following principles:

• run-off water had to be evacuated to prevent flooding in urbanized and waterproofed areas. It could also be infiltrated on site in less impermeable and less dense areas;

• wastewater had to be channeled away from residential areas without stagnating, as the pollutants it contains can cause nuisances or represent a health and epidemiological risk;

• wastewater must not be discharged directly into the natural environment (streams, rivers, coastal areas or subsoil through infiltration) without adequate treatment. In addition, wastewater must not infiltrate aquifers or water catchment areas likely to be used to produce drinking water;

• treated...