Approximately 80% of the water used for economic purposes returns to surface waters as sewage. In comparison to 1985, at the end of the 1980’s and the beginning of the 1990’s the total amount of sewage decreased by 12–23%. Of this total, the industrial sewage decreased 14–22%, mainly in the more industrialised voivoidships (MAP illustrating industrial and municipal sewage). This phenomenon, however, is not a permanent achievement but a temporary result of the recession.

Nearly two-thirds of all the sewage discharged into surface water is used for cooling processes in industry. The additional sewage heat influences the character of physio-chemical and biological processes and the state of ecosystems in the surface waters.

In 1995, of the 3,493 factories which underwent inspection, 54% did not have any sewage treatment plants and nearly 5% had plants which did not have sufficient treatment capacity. In 1995, 217 out of 860 Polish cities did not have sewage treatment plants and 105 cities had only mechanical treatment plants.

In the last several years, water pollution resulting from sewage from rural areas, is becoming an increasing problem. Out of approximately 75% of homes in Polish villages which are equipped with water supply, 4.5% have sewer systems, while 3.1% are connected to sewage treatment plants.

Non-point pollution also contributes to the pollution of surface waters. It is a type of pollution which results from soil erosion. Many substances, such as organic, phosphorous, and nitrogen containing compounds from artificial fertilisers, herbicides and pesticides erode, along with the soils, into the surface waters. This type of pollution occurs most frequently as a result of the work done in agriculture and forestry. It is estimated that over 50% of the nitrogen, 40% of the organic compounds and 30% of the phosphorus in river run-off comes from non-point pollution.

Another type of contamination results from atmospheric precipitation. As a result of the low buffer capacity of mountainous terrain in Poland (Karkonosze, Tatras, and Swietokrzyskie Mountains), the pH of the water in these areas is lower.

Salinated water is yet another surface water contaminant. This water comes mainly from the hard-coal mines. The salt load which contaminates the surface waters amounts to approximately 9,000 tons of sulphates and chlorides per day. In the basin of the Vistula River, two-thirds of this load is carried off while the rest remains in the basin of the Oder River.

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