The secret of clean drinking water is good raw water. "Helsinki enjoys excellent water. Its quality corresponds to the standard of the good ground water," says Ari Nevalainen, the communications manager at Helsinki Water. The treatment of the city's waste water is also first class.

Quality requirements have been set for Finland's drinking water and waste water at both national and EU level. The Finnish requirements are stricter than those of the European Union. Helsinki Water has also set its own quality requirements, which are stricter than those of the Finnish authorities.

Longest water tunnel in the world

The drinking water of those living in the Helsinki Metropolitan Area travels a long way from Lake Päijänne along the longest unbroken rock tunnel in the world for treatment at the water treatment plants in Helsinki. The tunnel, which is about 120 kilometres long, came into operation in 1982.

The quality requirements set for the drinking water apply to the contents of nitrate, iron and total organic carbon. "The quality of the water in Lake Päijänne these days is excellent in all respects, so the water treatment process is very light and natural and the amounts of chemicals needed are minimal," Nevalainen says.

Waste water in sustainable development

A new era in Helsinki's waste water treatment started when the Viikinmäki waste water treatment plant was completed in 1994. The plant, most of which is built inside the rock, is one of Finland's most significant environmental protection investments.

"The plant will guarantee that the waste water from almost one million inhabitants in the Greater Helsinki Area and from industry will be treated a long way into the future," Nevalainen states.

The principles of sustainable development were put into effect in the Viikinmäki waste water treatment plant. The biogas produced from the sludge is put to good use: the plant is self-sufficient in heating, while in electricity it is about 50 per cent self-sufficient. The sludge is also processed into soil products.

Fewer discharges into sea

Nevalainen says that the objectives of the waste water treatment are linked with the nutrient contents that are important with regard to the state of the Bay of Finland. Waste water includes a great deal of phosphorus and nitrogen nutrients which, when led to the sea, cause serious eutrophication.

"We have succeeded with the treatment targets. The Viikinmäki waste water treatment plant eliminates 95 per cent of the solid and oxygen-consuming substances and phosphorus in the waste water. The denitrification capacity is almost 90 per cent."

The condition of the sea areas off Helsinki and the internal bays has become much cleaner during the recent decades along with the improvement in treatment results. The amount of phosphorus finding its way to the sea has fallen to a third in ten years and the organic loading to under a half.

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The drinking water in Helsinki is first-class.