This paper will study how water analysis was a disputed knowledge in the 19th century. The study of scientific controversies and the role of experts related to analysis of water has a great interest in the study of 19th century science, its protagonists and its practices. Controversies related to the analysis of baths and spas were very frequent. Spas were a place across the borders from chemistry to medicine where distinct techniques, diverse interests and different traditions were discussed. Water analysis was not only a complex chemical operation but also one of the most controversial. This operation involved pharmacists, physicians, chemists and engineers who employed distinct techniques, pursued diverse interests and assumed different traditions. By analysing the water of the spa experts claimed the medical efficacy and the chemical composition of the bath.

This paper will study the wide range of interests related with baths and spas and some of the disputes between experts for controlling their analysis. The importance of some chemical elements dissolved in the water, the medical effects of taking a bath into the spa instead of employing bottled water, or the differences between natural and artificial water are an example of these controversies. Finally, we will study the development of chemical analysis in Spain focusing on the contribution of Antonio Casares (1812-1888). He was a prominent Spanish chemist who wrote several chemistry treatises and analysed some of the most important Spanish spas. By comparing some of his works we will study how the analysis not only involved disciplinary interests, but also economic and even personal ones.