Water is a key resource in society. People have always settled where water is available in good quantity and quality. Safeguarding this key resource is still a first priority in our societies. Living close to water is also today a favorite choice as can be seen on any map of population density or distribution of cities. A healthy environment requires a well functioning management of water.
In the world as a whole bad quality water and too little water is a growing threat towards human health and well-being and is the most urgent environmental challenge. On a global scale lack of safe water causes about a third of all child mortality. It is the cause of wars, starvation, and failure of harvests. Growing populations in the mega-cities in the developing world constitutes an especially serious water problem.
In this perspective the Baltic Sea region has good access to water. Germany and Poland have a runoff of some 1,200 m3 per person and year, a figure that is close to 20 times higher in the far north. On the consumption side, households today use some 200 liters per day, a figure that was only a few years ago considerably higher, and much higher in the countries in transition where water was not priced at all during the communist time. Likewise, industries are recently using water in a more economic way, as better technologies have developed during the last twenty years.
The largest threat towards healthy water is improper ways of getting rid of waste. At one time human sewage and food waste were too often emptied in the streets and in the nearest water course. Water downstream then became a carrier of diseases. Especially in the cities, the smell and sight was terrible as waste accumulated on the streets.
It was not until the late 19th century that infection of water by human sewage was properly understood and an acceptable system for management of sewage gradually developed. In the West such systems were installed on a major scale from the 1950s on. In Central and Eastern Europe improved and enlarged water works, sewage systems, and wastewater treatment plants have been a first priority after the systems change around 1990, and a very large share of environmental investments have been and still are devoted to aspects of water quality.
In this chapter the use and management of water are discussed. Water management is traditionally a task for engineers in the field of technology of hygiene. Today the scope of engineers has to be enlarged to include concepts of ecology and recycling.
In historical times little was wasted. Sustainability requires that we return to this approach, and regard waste as a resource to be recycled. A weak point in water management is the recycling of nutrients. Sludge from wastewater treatment plants is a major source of phosphorus, a nutrient which should be returned to farmland, to close the phosphorus cycle. Considering all aspects of water and the nutrients it carries is part of sustainable water management.