The layout of this study, designed as a randomized crossover clinical trial, is to evaluate the efficacy of an intervention with mineral-medicinal water from As Burgas (Ourense) in patientssuffering from fibromyalgia. This sample was randomly divided into two groups: group A and group B. In phase 1, group A had 14 baths in thermal water for a month and standard pharmacological treatment; group B, standard pharmacological treatment. Washout period is 3 months. In phase 2, group A had standard treatment and group B had 14 baths in thermal water for a month plus standard treatment. The Fibromyalgia Impact Questionnaire (FIQ) was used; this grades the impact of the illness from 1 (minimum) to 10 (maximum), which was measured in both phases. Twenty-five patients were included in each group and the study was concluded with 20 patients in group A and 20 in group B. The intervention group obtained, once the baths finished, a mean score of 60.3 (± 11.8) and the control group of 70.8 (± 13.0) (p < 0.001). Three months later, the intervention group presented a mean score of 64.4 (± 10.6) and the control group of 5.0 (± 11.3) (p < 0.001). We can therefore conclude that the simple baths with mineral-medicinal water from As Burgas can make an improvement on the impact caused by fibromyalgia.