SMHI - Water Protection Services
SMHI can provide data for the establishment of protection zones and safety regulations for surface water to supply safe areas for drinking water. An important point of departure for the delimitation of water protection areas in lakes and watercourses is to create a period of respite for emergency efforts in the event of an accident so that the water output can be stopped in time before the pollutant reaches the output point.
In order to establish protection zones around an area of surface water, it is important to know how much time it takes for a potential pollutant to reach the water inlet area: this is the so-called flow time.
After that, the limits for a primary and secondary protection zone can be developed. The primary protection zone is determined by the flow time of 0-12 hours and the secondary protection zone is determined by a flow time of 12-24 hours.
SMHI offers detailed calculations of flow times for watercourses and lakes. The methods used by SMHI take into consideration several factors and provide a more accurate assessment than the rough calculation methods reported in the Swedish Environmental Protection Board's handbook, which contains general guidelines for water protection areas.
This means that the water protection area's borders can be determined with greater accuracy.