Drinking water supply through the public water supply system
(the text below is based on the chapter Drinking water supply through the public water supply system published in yearbook Prague Environment 2004)
Fig. - Drinking water production since 1986 in respective water treatment plants
Source: PVK, a. s.
The public water supply system in Prague and the drinking water treatment plants for the customer drinking water supply has been administered by Pražská vodohospodářská společnost, a. s. since the beginning 1998. The joint stock company of Pražské vodovody a kanalizace, a. s. (PVK, a. s.) is the operator of the Prague’s water supply system.
Drinking water treatment plants
In 2003 the long-term descending trend in the water production continued. Compared to the situation in 2002 the production dropped by 3,308,000 m3 water i.e. by 2.3 %.
Compared to the previous year in the area of drinking water supply no substantial change happened in the output of water treatment plants.
Drinking Water Treatment Plant Podolí was severely affected by the flood in August 2002. In 2003 all consequences of the floods were rectified and the plant was returned to the shape capable of full operation.
Owing to the permanent decrease ion the water consumption the decision was made to use the Podolí Plant as a spare source only in future. Its functionality was verified in February 2003 when it supplied water into the distribution network for the whole month. In next years it is assumed the plant will be operated once or twice a year.
In 2003, when the Water Treatment Plant Podolí was under operation merely in February and October, it produced 2,211,000 m3 drinking water, that is its share of the total water produced in PVK, a. s was 1.5 %. It is a relatively small share, however, the water treatment plant forms a very important spare source to Prague. Compared to the situation in 2002 the production of the Water Treatment Plant Podolí dropped by 8,147,000 m3.
Drinking Water Treatment Plant in Kárané is located at the confluence of the Jizera River and the Labe River. It was commissioned in 1914 when it became the first water treatment plant providing Prague with innocuous drinking water.
Its maximum capacity is approx. 1,900 l.s-1. The water is pumped to Prague by means of three discharge mains 23 km in length each. A portion of the water produces is supped to municipalities and communities to the plant immediate surroundings.
The Water Treatment Plant in Kárané is the only one of three water treatment plants serving Prague, which a portion of water comes from groundwater sources from sand-gravel strata and artesian wells. Its other source of water is surface water from the Jizera River treated by the artificial groundwater recharge. Advantage of water from the treatment plant is its high quality. The drawback is its long-term as well as short-term limitations by weather conditions and the need of energy-demanding pumping to Prague.
The time dependence of water abstraction from classic (groundwater) sources is shown in Figure. It is obvious from the time dependence given that the deepest short-term drop happened in summer 2002 partly induced by the slated reduction in abstraction for the cementing of collecting mains and shutdown of pump stations for the planned replacement of pumps, and by the shutdown of a part of classic sources caused by flooding. Concerning the long-term development it is essential that recently the drop of these abstractions relates to the decreasing trend in water consumption.
In 2003 the Káraný Plant produced in total 31,769,000 m3 drinking water (summary of traditional sources and artificial recharge ones), which means 22.3 % of the total drinking water production of the PVK, a. s. that is a lower share then that in 2002 (annual decrease in production was 7,575,000 m3).
Drinking Water Treatment Plant Želivka – It is the most modern drinking water source to Prague having the largest capacity as well. It was commissioned in 1972. Its maximum output is about 7,000 l.s-1 yet due to the decreasing water consumption it has been utilised up to its half only. Besides Prague the plant supplies drinking water a part of the Vysočina Region and a smaller areas in the Central Bohemia Region.
This water treatment plant water source is raw water from the Želivka River accumulated in the Švihov Water Reservoir. The water reservoir was designed as a many-year reservoir with the usable volume of storage space 246 million m3 in between the spot heights 377.00 m and 343.10 m. The water level in the reservoir from January 1993 is shown in Figure. Since the beginning of 1995 a permanent trend in water level increase has been apparent and since January 1996 water in the reservoir has been fully swollen and only short-term drops in water level occur depending on precipitation. The fact also relates to the drop in water consumption and thus with the decrease of water production in the Water Treatment Plant Želivka in recent years. The extremely dry spell in 2003 incurred the lowest drop of level since 1996 down to the spot height 373 m yet when compared to the situation in the first half of the 1990s this is a low importance drop concerning the reservoir operation. In the course of the first half of 2004 the level got swollen back almost reaching the maximum level.
Raw water is treated by sand percolation filters with fast filtration. The filtered water is taken to ozonation, which improves organoleptic properties of water. Health innocuousness is provided by means of chlorine dosing.
Treated water is led to Prague through a shaft mains, which delivers water to the distribution reservoir in Jesenice. From the distributing reservoir water is delivered to the territory of the City of Prague in the area in between Písnice and Hrnčíře.
Major advantages of the source Želivka encompass the relative stability of raw water quality, substantial capacity of the source, and low energy demand due to the gravitational transport of water to Prague.
In 2003 the Želivka Water Treatment Plant produced in total 108,674,000 m3 drinking water, which mean 76.2 % of the total water production of the PVK, a. s. The plant production increased annually by 13,315,000 m3. This increase has a lot to do with the substitution of the production of the Water Treatment Plant Podolí, which was under operation for mere two months in 2003.
Besides the drinking water sources mentioned here above the company of Pražské vodovody a kanalizace, a. s. also operates an industrial water supply system, which delivers industrial water to enterprises in the Northeast part of the City. The abstraction station thereof is located on the Libeňský Island and it uses the Vltava River as water source. In 2002 floods the pump station was submerged and damaged. For the reason the industrial water supply system was shutdown and due to the great extent of damage it has not been put back under operation so far.
Tab. - Production of treated water in respective treatment plants of the PVK, a. s. in 2003
| Treatment Plant | Production [1,000 m3] | Share [%] |
|---|---|---|
Želivka |
108 674 |
76,2 |
Káraný |
31 769 |
22,3 |
Podolí |
2 211 |
1,5 |
Industrial water supply |
0 |
0,0 |
Total |
142 654 |
100,0 |
Source: PVK, a. s.
Water supply system
Because of complex topography the water distribution across the City territory is very demanding for technology. The drinking water supply system utilises 3,549 km of water mains (out of that 3,519 km are drinking water mains), 670 km of water branches, 40 pumping stations, and 71 distribution reservoirs of total volume 960,000 m3.
The water supply system features a relatively high failure rate due to its age, conditions of its construction, corrosion, material composition, and other effects. Approximately 1,000 km that is 30 % out of the total system of pipes are over sixty years old. In 2003 the number of opened accident pits, which had to be performed in order to provide for the Prague’s water supply system operation, accounted for 7,349, which is by 500 less than in 2002. In total 76 accidents of 1st category (water supply disruption to over 1,000 inhabitants or to important buildings and premises) and 280 accidents of 2nd category (water supply disruption to 300 to 1,000 inhabitants or to important buildings) were fixed. Compared to 2002 the number of accidents of 1st category rose by 28 and those of 2nd category by 92 incidents in 2003.
The thorough search for latent leaks of water from pipelines and the disruption of illegal abstractions brought a substantial reduction in water loss in recent years. The trend is depicted in Figure. The highest water loss was found in 1996 when it accounted for 46 % of the water for sale. In the subsequent years the loss has been decreasing year after year. In 2003 the loss accounted for almost 29 %.
Water consumption and supply
In 2003 total water production was 142,654,187 m3, out of that volume 14,066,266 m3 were supplied to clients located outside the Prague’s territory. All water consumed in Prague was produced in sources operated by PVK, a. s.
The tendency in the drinking water production since 1986 and in respective water treatment plants is shown in Figure. The graph clearly demonstrates still continuing long-term trend in every year decreasing water production lasting since 1991. 1996 was the only exemption when annual water production increased.
Percentage shares of respective water treatment plants on the total water production since 1986 are depicted in Figure. Within the period plotted the Water Treatment Plant Podolí recorded the highest drop in share of total production. In 2002 its share was 7.1 % while in 2003 it was mere 1.5 %. In 2003 in the case of the Water Treatment Plant Kárané its share of the drinking water produced annually decreased to 22.3 %. In 2003 the Water Treatment Plant Želivka attained the share of 76.2 %, which was a substantial increase compared to previous years.
The groundwater share of the total volume of the drinking water produced is demonstrated in Figure illustratively documenting that following a couple years of permanent growth each year its share has slightly dropped since 2002. In 2003 the share was 15 %.
Fig. - Time dependence of water abstraction from classic sources in Kárané
Source: PVK, a. s.
Fig. - Water level development in the Water Reservoir Švihov
Source: PVK, a. s.
Fig. - Share of respective water treatment plants of the total production of drinking water
Source: PVK, a. s.
Fig. - Share of groundwater of the total volume of drinking water produced
Source: PVK, a. s.
Fig. - Water loss in water supply system
Source: PVK, a. s.
Fig. - Diagram of the water distribution system of Prague and customers outside Prague
Source: PVK, a. s.