Drinking water quality
Drinking water quality is required to comply with the Regulation No 82 “Quality and Control Requirements and Analysis Methods for Drinking Water” issued by the Minister of Social Affairs on 31 July 2001 (hereinafter referred to as the Regulation No 82) originating from the Estonian Water Act and the European Union Drinking Water Directive 98/83/EC.
An increase in the number of people drinking tap water continued as a positive trend also in 2014 – in the previous years the proportion of those drinking tap water has grown from half of the end-users to 80-90%. The growing trend of drinking tap water is definitely based also on the improvement of tap water quality and taste, although those have not gone through huge changes over a year, still the ratings given by the end-users have constantly been improving year-on-year.
The water quality is monitored following the Drinking Water Quality Monitoring Programme approved by the Health Board. The Programme for the years 2013-2015 determines the sampling spots, sampling frequency as well as the parameters to be analysed. Samples are taken from the raw water (Lake Ülemiste, the catchment area thereof, and ground water) treatment process, bore-wells, as well as the customer taps.
Conditions for using ground water have been determined in the permits for a special use of water HA0132 (L.VV/323855), TL0687 (L.VV/322982), HA0382 (L.VV/320972) and HA1106 (L.VV/320980) issued to the Company. Although the usage of ground water is limited by the permits for a special use of water, it is possible to cover the ground water demand and still have sufficient reserves to partially replace some of the supply by ground water in case there should be any problems with regard to the drinking water supplied from Ülemiste Water Treatment Plant.
Drinking water quality analyses are carried out by the Company’s water and microbiology laboratory, which is one of the largest water laboratories in Estonia. The quality of the analyses is guaranteed by the certified collectors and laboratories accredited by the quality management system (EVS-EN ISO/EC 17025 standard), using modern equipment and employing professional staff. In 2014, our water and microbiology laboratory performed a total of 97,000 analyses.
Treated water quality at Ülemiste Water Treatment Plant
Almost 90% of our consumers are supplied with drinking water produced out of surface water. Although Lake Ülemiste is the main drinking water source for Tallinn, the natural catchment area of the lake itself is small. To provide sufficient water source, an extensive water catchment system has been established. The quality of surface water is mostly affected by the weather and geographical location of the catchment area. Thus, the entire water catchment system is affecting the quality of surface water. Our main challenges are caused by the weather – floodings and changes in the raw water due to long winter periods.
In 2014, the treated water quality at Ülemiste Water Treatment Plant was compliant with the requirements of the Regulation No 82.
Surface water quality
The water quality in surface water sources is monitored in line with the programme established based on the conditions of the permit for a special use of water. In 2014, the quality of raw water in the treatment system complied with the class A2 requirements of the European Council Directive 75/440/EC.
To ensure compliance, the raw water quality indicators are analysed once a day at the intake to the treatment system. The raw water pollution indicators, such as total phosphorus and total nitrogen, are analysed once a week. Furthermore, an in-depth analysis of raw water is carried out once a month in accordance with the Drinking Water Quality Monitoring Programme.
Based on the results of the analyses we assess the changes and processes in the catchment area and decide upon the supplementation of the water supply in the lake.
In 2014, the permanganate oxygen demand was significantly lower than in previous year. Also the water colour parameters in raw water were lower.
In 2014, raw water quality was exceptionally good, which brought about the reduced chemical consumption and contributed to achieving the good drinking water quality. This was caused by dry summer, due to which the water did not wash nutrients from soil into water bodies and surface water quality improved across the whole water catchment system.
Ülemiste sanitary protection zone
Lake Ülemiste is the drinking water source for more than 400,000 people living in Tallinn and its nearest surroundings. To protect the water body providing drinking water, Ülemiste sanitary protection zone was formed in line with the Water Act § 36 (1). Pursuant to this act, protection shall be provided to the area (where stricter than usual environmental requirements and consequent restrictions apply) of water bodies, which are used for supplying drinking water, and the surrounding sanitary protection areas.
The sanitary protection zone includes the lake, the water catchment facilities thereof, the bank reinforcement facilities and the area surrounding the lake, which must be kept in its natural condition. The sanitary protection zone is marked and protected with a fence. Under the Water Act, entry into the sanitary protection zone is permitted only for persons performing duties related to environmental supervision and health protection, servicing of water catchment facilities and forest maintenance, mowing of grass plants and water monitoring.
Over the last years, human and development activities, construction of motorways and airport activity have become more intensive in the areas surrounding the lake and this has increased the environmental risks on a drinking water source.
As Ülemiste Water Treatment Plant does not have an alternative raw water supply source today, we deem it extremely important to ensure natural balance around the lake. Free public access to the drinking water reservoir may increase the risk of polluting the water source and deteriorate water quality.
Efficiency of the water treatment process
Ülemiste Water Treatment Plant treats water applying a treatment scheme that is used world-wide. We use ozone in the treatment process to improve the quality, odour, colour and taste of water and this has enabled us to reduce the volume of chlorine to approximately a tenth over a decade. Drinking water must be safe and must not contain any pathogens. Therefore we add small amounts of chlorine in the drinking water, which is completely safe for human health, but at the same time an extremely effective measure to protect water against bacteria on its way through the network up to the customer taps. In 2014, the water quality in the lake was exceptionally good, which consequently reduced the cost of chemicals and ozone used.
Depending on the surface water quality of Lake Ülemiste, the law determines the physicochemical treatment of surface water to ensure the quality of drinking water – prechlorination, coagulation, sedimentation, filtering and disinfection.
To improve the water treatment process performance, four filters were regenerated in 2014. To reduce the load of filters, a water recirculation system of clarifiers’ sludge catcher was built at the old water treatment plant, which enables additional treatment of water with high turbidity after flushing process. In order to improve the reliability of ozonation process, critical spares in ozonators’ power circuits were replaced.
Ground water quality
Approximately 10% of consumers in Tallinn are supplied with water produced from the Cambrian-Vendi and Cambrian-Ordovician aquifers. Ground water is supplied in the districts of Nõmme, Laagri, Merivälja, Pirita and Tiskre in Tallinn, Tiskre village in Harku Rural Municipality and City of Saue. Harku country town, and the settlements of Muuga and Kallavere in the City of Maardu have been taken to surface water supply.
According to the EU Water Framework Directive (2000/60/EC), the qualitative or chemical condition of ground water is regarded to be good if the concentration of pollutants does not indicate an inflow of salty water or other water, nor does it exceed the respective quality standards. In 2014, the quality of drinking water at the borehole pumping stations complied with the requirements of the Regulation No 82 , issued by the Minister of Social Affairs. There were no cases of ground water pollution or potential pollution demanding the notification of the City of Tallinn and the Health Board.
We monitor all of the quality parameters established in the permits for a special use of water and the drinking water quality monitoring programme, and if needed, the ground water goes through a treatment process. We monitor the quality of treated ground water (concentration of iron, manganese and ammonium) in 20 ground water pumping stations on a monthly basis.
Ground water in Northern Estonia (Cambrian-Vendi aquifer) contains natural radionuclides. The natural radioactivity of Estonian ground water has been thoroughly studied by the Geological Survey of Estonia as well as the Estonian Radiation Centre. To assess the health impacts of radioactivity, the Radiation Centre together with the Health Board carried out a health risk assessment in Tallinn ground water areas in 2010. Based on the results of the risk assessment, any health damage of accidental nature resulting from the content of radionuclides in the water of Cambrian-Vendi bore-wells is unlikely. Additional information on this topic is available on our webpage www.tallinnavesi.ee or on the Health Board’s webpage www.terviseamet.ee.
Ground water treatment
Ground water used for producing drinking water usually belongs to the quality class I-III. Ground water from Ordovician-Cambrian aquifer usually belongs to the quality class I and does not need any treatment. However, ground water from Cambrian-Vendi aquifer in the quality class II or III and serving as the main drinking water source requires treatment. The main reason is mostly a natural excess content of iron, manganese or ammonium resulting in higher turbidity of water than usual.
In order to supply compliant drinking water, we treat ground water by using filtration and aeration to remove excess iron, manganese and ammonium from the water. Filtration uses pressure filters installed in the bore-well pumping stations. Pressure filters are used to aerate and filter raw ground water. The Water Act foresees the preservation of ground water as similar to its natural conditions as possible, therefore, no chemicals are used. The samples taken after the ground water treatment process indicate a significant decrease in turbidity as well as in the content of iron, manganese and ammonium, an improvement of colour and stability index and an increase in oxygen content.
To improve the water quality in the City of Maardu, the city has gradually been transferred to surface water supply from Ülemiste Water Treatment Plant. All bore-wells in Maardu are currently in reserve and there is no consumption of ground water. The bore-well pumping stations switch on only in case the pressure of drinking water from Ülemiste is insufficient; also, the bore-wells are used to keep certain water supply. 100% of the water samples taken in 2014 from the ground water bore-well pumping stations in Maardu were compliant with the requirements. In addition to Maardu, also the bore-well pumping station areas of Rukkilille and Karikakra in Harku borough were taken to surface water supply from Ülemiste Water Treatment Plant starting from 1 June 2014. A booster pumping station was built in the area to ensure the required water pressure.
Drinking water quality in the network and customer premises
Tap water in Tallinn and Maardu is of a very good quality and it is safe to drink it. In terms of quality, the year 2014 did not differ from the previous periods. During the year, we took samples twice a month at the sampling points agreed with the Northern Department of the Health Board.
The best ever result, where 99.80% of all water samples complied with the standards, means that in 2014 we detected non-compliances only in 6 samples of the total of 2,946 samples taken from customer taps. The non-compliances were mainly related to higher iron and turbidity parameters caused by the conditions of the water network. We immediately reacted to all non-compliances.
100% of the 144 water samples taken in Maardu in 2014 complied with the standards. Before the connection with Tallinn water network, the quality compliance of drinking water in Maardu was only 33%.
Maintenance and investments related to the water network
We are constantly performing maintenance and renovation works on the network to retain and improve the drinking water quality. We regularly clean and flush the water network to guarantee high drinking water quality for the consumers. During the cleaning process the sediment build-up is removed from the network serving as one of the important methods improving water quality in distribution networks. In 2014, air-scouring pipe cleaning method was carried out on 145 km of water network.
Investments in replacing old water pipes have facilitated an improvement in water quality in customer premises and a more efficient use of water resources. 5.6 km of water pipes were renovated in 2014.
