Summary:

In 1998 the water intake from the Rudawa river for water supply purposes of Krakow was secured by storage reservoirs with a total volume of 981 thousand m3. The reservoirs are designed to improve the quality of water supplied to the Water Treatment Plant (WTP). Water collected in the reservoirs acts as supply used when water quality in the river deteriorates. Simultaneously the water is purified in these reservoirs. The article presents the impact of the reservoirs on the change of water turbidity and colour during the first 11 years of the exploitation of the reservoirs (1999-2009). The analysis was based on the results of the research carried out in five sites of the technological line, from the intake through the storage reservoirs to the raw water well (Młynówka, inflow to the reservoirs, outflow from the reservoir 1, outflow from the reservoir 2, the well of raw water located in the area of the WTP). The reservoirs had beneficial effect on the reduction in water turbidity in the analysed multi-year period. In the raw water well the average water turbidity value was lower than the turbidity of water drawn from the
Rudawa river (Młynówka) by 55,33% and the scope of the changes narrowed from 1-847 to 0,8-126 NTU. On the other hand, the reservoirs have little effect on the change in water colour. Because water from the Rudawa river is rich in nutrients, a slight increase in colour may be observed in the reservoirs due to periodic algal blooms. The average colour value of water drawn from the Rudawa river (Młynówka) was 14 mg Ptdm-3 and varied from 4 to 40 mg Ptdm-3, whereas in the well of raw water the average value was 13 mg Ptdm-3 and ranged from 5 to
25 mg Ptdm-3.