Some small islands are often confronted with water shortages: their limited size, topography, low density plant cover, scarcity of springs, poor water infiltration into groundwater, inadequate geology, or even the lack of rain, are likely to cause serious shortages in water availability. Reserves are limited to a thin layer of water on flat islands, groundwater is vulnerable to tides and the rise of saltwater infiltration accentuated by climate change and sea level rise. Higher islands potentially have larger water resources, but their storage capacity remains limited due to the lack of dedicated space or infiltration. access to drinking water on islands is therefore very uneven, as fresh water quality can be affected by the infiltration of seawater in the groundwater, or by pollution due to agricultural, domestic, or touristic activities.

Other islands that are less exposed to water shortages (with heavy rainfall or pipelines, etc.) may however be faced with misuse, over-use or storage problem.