Two sites in the north of Guernsey will likely be used by the States for a new reservoir and to store inert building waste.
Black Rock, near the Bridge, will become a waste disposal site while Les Vardes Quarry, also in St Sampson, will be used for freshwater storage.
The Committee for the Environment and Infrastructure (E&I) hopes the decision will provide better resilience and future proof the Island.
President of E&I Lindsay de Sausmarez said: "I am really pleased that the States has made two important strategic decisions."
Until the Black Rock site is available, the States will continue to stockpile inert waste at Lounge Houge.
Les Vardes will be the preferred location for freshwater storage, once quarrying activities are finished.