The ratio between effective water use and actual water withdrawal. In irrigation, it represents the ratio between estimated plant water requirements (through evapotranspiration) and actual water withdrawal.

The upper surface of the zone of ground water.

Physiological stress experienced by a plant as a result of a lack of available moisture or a low water potential in the surrounding soil; an instance of this. Economic or political pressures in a country or region as a result of insufficient access to fresh water.

The ratio of total water withdrawal to the water availability including environmental flow requirements. Higher WSI values lead to decreasing water security.

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.

The reliable availability of an acceptable quantity and quality of water for health, livelihoods and production, coupled with an acceptable level of water-related risks.

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, water-related disasters, and for preserving ecosystems.

Vegetation, and specially aquatic plants, can assist in removing sediments and nutrients and other impurities from water.

An excess of water on top and/or within the soil, leading to reduced air availability in the soil for long periods.

A situation where powerful actors are able to take control of, or reallocate to their own benefits, water resources already used by local communities or feeding aquatic ecosystems on which their livelihoods are based (Mehta et al., 2012).