Nitrate contamination of aquifers in rural areas of Mallorca and the Balearics has principally been attributed to the intensive or inappropriate agricultural use of fertilisers, but the latest revision of the Balearic Islands Hydrological Plan (PHIB) highlights another cause - the proliferation of houses on rustic land.
The plan refers to sources of diffuse contamination without a determined point of origin and which is in large areas where control and detection are difficult. These sources are escapes from sewage networks and from houses on rustic land that do not have a connection to the sewage system and have non-sealed septic tanks or cesspits.
"This results in an increase in the concentration of nitrates in groundwater and can cause an increase in the excessive contribution of inorganic nutrients. It is necessary to prevent this contamination in order to protect human health and ecosystems, especially aquatic ones."
The plan has measures to protect underground water resources against agricultural contamination. It is urging municipalities to evaluate and list improvements to their sewage networks so as to prevent leaks. In the case of isolated houses on rustic land, the plan requires the use of autonomous wastewater treatment systems and sets out requirements.
"However, the implementation of measures and, above all, the fulfilment of environmental objectives are taking place at a slower pace than expected. Additional measures are required ... . It is necessary to come up with an inventory of isolated homes not connected to the sanitation network to check whether they actually have an autonomous purification system."