Water is an essential element for Humans that brings many benefits for health and well-being. However if it's not controlled and proper for consumption, water can be life-threatening for humans. Water used at hydrotherapy establishments (HE), is a natural mineral water (NMW), that doesn't undergo any treatment and remains as found at spring. NMW isn't sterile water but, in normal conditions, the micro-organisms that are presents are harmless for bath users. Thermal baths are places of population influx and therefore must be periodically controlled, monitored and followed-up to guarantee the safety and quality of the services. This surveillance must be done by the owners of the establishments and supervised by the Public Health Department, Public Health Unit and Public Health Regional Laboratory, accordingly to the legislation and directives of the baths water quality control program of the Directorate General for Health (DGS). The sanitary surveillance done at HE by the Health Authority (HA) is composed of four aspects: hygienic-sanitary (guarantee the correct functioning and hygienic conditions at the facilities); technological (ensure the quality and maintenance of the equipment and procedures); analytical (periodical water samples collection to analyze the quality of the water and verify if the results provided by the bath's concessionaire are accurate and respect the reference values); epidemiological (epidemiological studies to see the relation between health and the bath uses). In case of failing to fulfill either one of this areas, the violation must be communicated to the responsible entity, as establish by DGS. Due to the interaction between this four areas, a breach in one of them can compromised the others thus the objective of the sanitary surveillance done by the HA in harmony with the HE is the way to assure and oversight the quality of the facilities and the waters used in the thermal springs treatments in order to avoid any disturbance potentially harmful to its users.