Abstract Heterogeneity of volcanic materials that constitute the Canary Islands (Spain) means that mining work in water galleries excavated on these islands, drilling into the terrain for many kilometres, is very challenging. They are composed of materials that vary significantly in terms of cohesion, ranging from very consolidated to loose and highly unstable. Water galleries have been key in the development of the Canary Islands, in order to obtain drinking water from the aquifer. Generally, aquifers are located in mountainous areas with difficult access, which complicates the drilling work. This article analyses the main geotechnical problems encountered in the construction of subterranean water galleries in the Canary Islands, as well as possible solutions to these problems, so that these can be applied to similar territories. As a general conclusion, the instabilities inherent in volcanic materials affect this type of work, and it is necessary to take specific measures for each type of geotechnical risk, as proposed in this article. Spain (Spain islands kilometres challenging cohesion unstable aquifer Generally access territories conclusion risk

Abstract Water galleries are mines that seek to supply drinkable and irrigation water from the aquifer, in order to meet the demand for water in the Canary Islands. This sort of work entails a series of health risks in the form of gases. This document compiles three different studies on the gases that can be found in water galleries in the Canary Islands, having divided the document as follows: 1) the presence of carbon dioxide in 13 galleries in operation on the island of Tenerife; 2) the presence of radon gas in galleries on the islands of Tenerife, El Hierro and La Palma; and 3) the incidence of gases that are harmful to health in a thermal water gallery on La Palma. The results have shown that, in general, the water galleries contain concentrations of gases which are toxic to human health, such as radon, where average radon values measured with both passive detectors are from less than 800 Bq/m3 to around 10,200 Bq/m3. Therefore, it is important to protect the health of the workers who undertake the maintenance of these installations.