William Withering (1741-1799) was an English physician, botanist, physician, and geologist. His father was a surgeon, and he entered the University of Edinburgh in 1762 to study medicine, completing his studies in 1767 and returning to England to open a private practice in Stafford. While in Stafford, his interest in botany grew even more when he married Helena Cookes. He published several treatises on botanic, such as The Botanical Arrangement of all the Vegetables Growing in Great Britain and An Account of the Foxglove, and Some of its Medical uses, through which he won a position at the Medical Hall of Fame. In 1783 he was diagnosed with pulmonary tuberculosis and traveled to Portugal several times for treatment.

He had a strong interest in Portugal, especially the tropical and semitropical plants of the Algarve, as well as the climate which improved his health. In one of his visits to the Lusitanian territory, it was requested by the Court of Portugal for him to analyze the Thermal Waters of Portugal, especially the Thermal Springs at Caldas da Rainha. In 1795 it was published in Lisbon the treatise entitled A chemical analysis of the water at Caldas da Rainha, both in Portuguese and English. The treatise deals with temperature, odor, color, taste, depositions, the Specific Gravity, the Elastic Fluids, reagents (including Pao Brazil, vitriolic acid, distilled vinegar, nitre of silver and others) and the evaporation. The treatise was considered the first genuinely scientific analysis of Portuguese waters and influenced other studies that were done within a few years, such as that of Francisco de Paula Tovar, which included chemical analyses to fill in the gaps in earlier work.

As for Portugal, a total of six copies are present: five at the Portuguese National Library (BNP) and one at the Central Naval Library.