Quality of drinking water

Residents of the Helsinki metropolitan area drink tap water that is of excellent quality. Most of the raw water for the Helsinki metropolitan area comes from Lake Päijänne by a tunnel running over a distance of more than 120 kilometres. The multi-stage treatment process of our water treatment plants produces high-quality supply water. We make sure that there are no substances or microbes in the water that are harmful to health.

Water quality

The water quality in the Helsinki metropolitan area is high. The household water we produce easily fulfils the quality requirements and recommendations set by the Ministry of Social Affairs and Health in its related decree (1352/2015). In addition to HSY’s own control samples, the health protection authorities of municipalities monitor the water quality in the supply network in accordance with the control research programme.

We monitor the microbiological, physico-chemical and sensory quality of water provided by the Pitkäkoski and Vanhakaupunki water treatment plants every weekday in our laboratory. In addition to this, we supervise the water quality in the water supply network. We carry out approximately 40,000 water analyses each year to monitor the quality of raw water, the treatment process and supply water provided by the plants, as well as the water quality in the water supply network.

Water quality table The water quality table is updated four times a year.

A small amount (0.35–0.50 mg/l) of chlorine is added to the water pumped into the network from HSY’s water treatment plants as bound chlorine, or chloramine. Chlorine protects the microbiological quality of the water in the distribution network. Chlorine is gradually used up (oxidised) in the network, with samples taken containing 0.03–0.5 mg/l of chlorine.

The concentration is affected by the water temperature and the time spent in the network. Raw water is at its coldest in the network during winter, and chlorine is then preserved better in the distribution network than when the water is warm. Most people do not smell or taste low concentrations of chlorine, but some notice even small changes. If the smell or taste is disturbing, the water can be left standing in an open container in the refrigerator or on the table before use. Another option is to boil the water, allowing chlorine to evaporate faster.

Water hardness

The household water in the Helsinki metropolitan area is soft, which means that its lime content is low. This is why less detergent can be used than with hard water. In the Helsinki metropolitan area, the hardness of water ranges from 2.7 to 4.5 °dH, depending on the plant.

Degree of water hardness

Very soft = 0–2 °dH
Soft = 2–5 °dH
Medium hard = 5–10 °dH
Hard = 10–21 °dH