THE history of water supplies in England is a poorly documented subject. Although various accounts of the history of water technology, and learned articles on the political and administrative aspects of water supply have been written, the history of water in relation to public health remains largely unexplored. As this is, especially concerning the nineteenth century, a voluminous subject, the present paper attempts no more than a broad survey of the process by which water came to be recognized as a vital element in public health, of the gradual discovery and application of criteria for water purity, and of the means by which supplies satisfactory in quantity and quality were obtained. The roots of the modern concern with environment and its effect on health lie in the eighteenth century, and in this period the first indications of interest in the quality and physical effects of water are found. Health and cleanliness were treated as personal matters in the eighteenth and earlier nineteenth centuries: in the first parliamentary inquiry into water quality in 1828 there is little evidence of any wider concern with the health of the general population. It was only in the later 1 830s and 1840s that the idea of public health in its widest, or modern, sense began to gain currency, and only in the second half of the nineteenth century that the term came to have, for certain social elements, a further dimension of public morality as well. It is against this background of movement from an individual to a social concern that the development of modern standards of water services must be viewed. The evolution of the public health idea during this period is reflected in the nature and quantity of primary sources. These are sparse for the eighteenth century, but plentiful by the second half of the nineteenth. The sources for the latter period are also more familiar, and therefore have been treated more cavalierly in this paper: the intention has been more to illuminate less familiar aspects of the water question than to present a definitive history. The geographical scope of this account has been limited to London, partly for convenience, but also because the experience of the capital was crucial in influencing the development of medical and legislative concern with water.