In Greenland surface water is used as a drinking water resource. Each settlement has its own separate supply of drinking water. In some places, there is an abundance of water, but in many places there is a severe scarcity. This is particularly in the settlements placed on small islands and in the settlements placed in the High North, where the water is frozen in a large part of the year. In those places, technologies such as reverse osmosis is sometimes used to extract sea water for drinking water. Also, in some places, ice is being thawed for drinking water during the winter. Both processes are very energy consuming and expensive. The drinking water is piped in many places. Piping in Greenland is difficult due to the temperature and the climate, so heating is necessary to keep the drinking water fluent in the pipes. In the places where there is an abundance of drinking water also sometimes the water is just pumped at a high speed through the pipes to keep it flowing, instead of heating. That is more energy efficient. In the small settlements, self-hauling from central houses is common. The drinking water is being treated, usually by chlorination. In the places where fish factories are active, UV treatment is also implemented to meet the high international standard of food production industries.