Water, an essential nutrient, is often ignored in reports of dietary surveys and nutrition. Although it is ubiquitous in foods and beverages, the attention is often focused on the minerals or calorific values of the fluids imbibed rather than the water per se. Water is often taken for granted by many in Western countries due to its abundant availability through water systems. In developing countries, however, water and sanitation raise significant problems. This review overviews (i) the global perspective of the potable water supply, (ii) human rights and water, (iii) dietary guidelines and sources of water and (iv) the physiology of water balance. Gaps in knowledge and understanding around hydration and water requirements are also discussed. Nutritionists are urged to look at the bigger picture of the global water supply and to use good judgement and common sense when advising on water requirements.