Water is Tenerife's most valuable resource. Because of the Island's volcanic characteristics and its porous, permeable ground, much of the rainfall filters into the earth, pushing its inhabitants to make use of their cunning in order to get underground and access these subterranean watercourses. Weirs and dams are another key element, though less numerous than wells and canals as a means for obtaining fresh water on a land surrounded by salty sea water. More than 80% of the water that is consumed in Tenerife is sourced from its network of 1,700 km (1,055 miles) of canals and 500 active wells.
Tenerife's ground is highly permeable on the surface, giving way to an impermeable basal layer deeper down. Rainfall and moisture condense and filter through the earth to the underground aquifers at the basal level. These huge subterranean pools are the key to survival as they guarantee Tenerife's population a source of fresh water.
The Island Hydrology Plan has been in place since 1997, analysing consumption and studying ways to increase water production. The greatest water consuming sector is agriculture, followed by the population's supply needs. Some of the options being considered include desalting sea water and purifying waste water to be used in irrigation. The first desalination plant began operating in the south of Tenerife in 1998. Tenerife also has plants for improving underground water quality by removing harmful minerals from water destined for human consumption.