The energy possessed by a mass, e.g. a body of water, by virtue of its being raised above a particular datum point, usually taken as either sea level or local ground level. The energy may be released when the mass is allowed to fall to a lower level, and may be harnessed, e.g. in the case of water by powering a turbine in a hydroelectric scheme. Elevation head is the energy possessed by a unit weight of water at a point, due to this cause. See also bernoulli equation; darcy’s law; pressure head.