The capacity of a population to safeguard sustainable access to adequate quantities of and acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability. (UN-Water)

Drought refers in general to a period of water shortage, but there are many types of definitions, including:

• Meteorological – when precipitation departs from the long-term normal
• Agricultural – when there is insufficient soil moisture to meet the needs of a particular crop
• Hydrological – when deficiencies occur in surface and subsurface water supplies
• Socio-economic – when human activities are affected by reduced precipitation and related water availability.