Arbejdsrapport fra Miljøstyrelsen, 6/2006 – Erfaringer med rensning af drikkevandet i små vandforsyningsanlæg

Erfaringer med rensning af drikkevandet i små vandforsyningsanlæg

Summary and conclusions

A major part of the 70,000 small private wells (water supplies) in Denmark have problems with the quality of their drinking water. Investigations carried out by Geological Survey of Denmark and Greenland - GEUS in 2000-2002 prove that for pesticides, nitrate and bacteria the drinking water standard is in many cases exceeded.

When it has been demonstrated that the drinking water standard has been exceeded for a private well, the owner has the following solutions to the problem:

1 Renovation of the facility.

2 Establishing a new well.

3 Connecting to a public waterworks.

4 Establishing advanced water treatment.

Traditionally, the choice is between the first three. However, in some areas connecting to a waterworks is difficult and if the possibilities for solving the water quality problems by renovating or by establishing new wells are limited, treating the drinking water for nitrate and/or pesticides can be a possible solution.

Danish experience from treatment of nitrate and pesticides in small water companies is rather limited and there is a need to consider the possibilities. As technical investigations have formerly been carried out abroad and the Danish administration is well-known, this project will primarily focus on the administration abroad and the technical possibilities in Denmark.

The project consists of two parts. The first part focuses on gathering of knowledge about foreign legislation and administrative systems including experience from their use. Furthermore, experience from facilities for treating nitrate and pesticides in small private wells in Denmark has been investigated by contacting suppliers, users and municipalities.

Small suppliers and water treatment facilities have been investigated in the USA, Germany, Norway, Sweden, England and Wales and The Netherlands. Both the USA and Germany have certification schemes for water treatment facilities for private well owners. Both certification schemes contain elements which will be relevant if a similar scheme should be introduced in Denmark.

In all the investigated countries, the responsibility for the drinking water quality lies with the owner of the facility. It is common to recommend that maintenance contracts are entered, but it is not compulsory.

Approximately 500 nitrate facilities have been sold in Denmark and mounted on small private water supplies. Most of these have been installed without permission from the municipality, so it is not checked whether nitrate filters are an appropriate solution to problems with the drinking water quality.

Two municipalities who have given permission to install nitrate filters were contacted. Both municipalities express a major need for supervision from the authorities and for certification schemes for the facilities.

In the second part, the administration of water purifying plants for small water companies is assessed. For this purpose, two alternative administrative models have been set up, and advantages and disadvantages are assessed.

When a water supply facility encounters contamination it is, in principal, the owner who decides how to solve the problem. Which solution will be the most suitable both technically and financially depends on the following:

the nature of the contamination
the design and condition of the well
groundwater conditions and the possibility of finding pure/clean water
the development of the public waterworks in the area.

The financial aspect can often only be assessed by obtaining quotations for one or more solutions.

The type of treatment facility depends on the type of contamination found. Increased levels of nitrate can be treated with an ion exchange facility. Water treatment is not considered an appropriate solution for microbial problems, because they are often caused by faults in the technical construction of the facility. These problems should therefore be solved by renovating the facility. Similarly, the use of charcoal filter to remove contents of pesticides is only an acceptable solution when the groundwater aquifer is contaminated.

A number of questions need consideration if there is a wish for establishing treatment of water in small private water companies to a higher extent than today.

1 Assess the need for support to the municipality administration by publishing guides and information material on the specific questions which are attached to administrating small water supply facilities.

2 Assess the need for preparing information material to owners who encounters water quality problems, explaining their possibilities.

3 Assess the need for establishing a certification scheme which, among other things, shall ensure that the treatment is sufficient and that the facility is safe, user friendly and environmental friendly.