The IPCC Working Group II (2001) Third Assessment Report identifies sea level rise as one of the most important coastal impacts of global warming, and identifies several key impacts. A number of these are particularly relevant for water utilities located in coastal areas, including: 1) lowland inundation and wetland displacement; 2) altered tidal range in rivers and bays; 3) changes in sedimentation patterns; 4) severe storm-surge flooding; 5) saltwater intrusion into estuaries and freshwater aquifers; and 6) increased wind and rainfall damage in regions prone to tropical cyclones.

These impacts are particularly likely to affect water utility infrastructure. For example, there could be impacts on water intakes located in transition areas between freshwater and saltwater interfaces of both surface and sub-surface systems. Sedimentation patterns in estuaries and deltas depend strongly on tidal patterns, storm surges and flow conditions, whose changes could affect utility supplies.

Saltwater intrusion into freshwater aquifers is already a problem in many coastal communities, primarily due to overdrafting of those groundwater supplies. Because of the higher density of saltwater, a rise in sea level could result in a disproportionate loss of freshwater aquifers in coastal zones due to the intrusion of the saltwater wedge.