Water treatment process

In Ülemiste Water Treatment Plant, surface water is treated by using environmentally friendly and modern technologies, and then supplied as a high-quality drinking water to the citizens.

Water treatment

In order to turn lakewater into a high-quality drinking water, it undergoes a thorough treatment. The whole water treatment process lasts for approximately 15 hours.

  • Raw water intake

Lakewater is pumped into the plant.

  • Mechanical treatment

Larger debris, algae and plankton are removed from the lakewater by using screens and microfilters. The fish are also left behind the first screen, which stops them from getting into the plant. The debris, algae and plankton removed from water are discharged into the sewer.

  • Chemical treatment

1. Ozonation
Ozone is a specific type of oxygen that improves water quality and colour, and gives it a better taste and odour. Furthermore, ozone kills microorganisms and bacteria that could harm humans. Ozone is not hazardous for humans.

2. Coagulation – adding special water treatment chemical
Coagulant is a substance that concentrates around particles in water, making them larger and heavier. As a result, the flakes that have become heavier sink to the bottom of the basin and can be flushed into a sewer.

  • Filtration

This means taking out tiny particles that remained in water after removing the flakes. For this purpose, dual-layered sand filters are used.

  • Chlorination

Chlorine is a chemical that is safe for human health in small quantities and helps to maintain the water quality in the city network.

Drinking water which is treated from surface water needs to be disinfected before it is pumped into the public water network, for which purpose chlorine compounds are used. The concentration of free chlorine in water discharged from the water treatment plant shall be in the range of 0.2mg/l…1 mg/l (Ministry of Social Affairs Regulation No 61). Drinking water quality requirements are in accordance with EC drinking water directives and WHO (World Health Organisation) requirements. The aim is to ensure that the quality of drinking water is maintained throughout the supply system and that the water is safe to drink.

  • Clean water

From the treated water basin drinking water is pumped into the network. Pumping stations are built around Tallinn so that the water would reach all the citizens.

Did you know that …?

  • … almost 90% of drinking water in Tallinn is produced from surface water. 10% of the consumers drink regional groundwater.
  • … if only groundwater would be used for drinking water purposes, then at today’s consumption the existing resources would be used up in 30 years.
  • … the main water source of Tallinners is Lake Ülemiste. The total volume of the lake is 33 million m3 but the volume used for treatment is ca 17 million m3.
  • … it would take 9 months for the Ülemiste Water Treatment Plant to treat all the water in the lake.
  • … the average amount of drinking water treated at the plant is 60 000 m3 a day. The maximum amount of water that the plant could treat, though, is 120 000 m3 of water a day.