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.