In 1846 Faraday gave a lecture on the ‘Cohesive Force of Water’. This property of water is still important. The Laplace formula for the pressure developed by the surface energy of liquid water in capillaries, P = 2 γ/r, where γ is the surface energy (72 x 10^-3 J m^-2) and r is the radius, is well known, and appears in physiological textbooks. The surface energy of water was an important part of the preclinical medical course seventy years ago, but has largely disappeared from the curriculum in the latter decades of the twentieth century. Biocomputation and molecular modelling were proposed eleven years ago as submicroscopic physiology (Widdas, 1993). Cellular biology and the properties of water, are reinvigorated by the application of the Laplace pressure to biological systems. Its use in muscular contraction was suggested by Bernstein in 1908, and Weizsacker (1914) when working with A.V. Hill showed that muscle twitches were completely blocked by ethanol above 6%. This concentration of ethanol inhibits glucose exits in erythrocytes by lowering the surface tension of water (Widdas & Baker, 1991).The physical chemical problems, which are involved if two energy sources contribute to the same mechanical function as proposed by Widdas & Baker (2001) can now be more clearly defined. It is now proposed that there should be a reconsideration of the contribution of the surface energy of water in supplementing that of ATP hydrolysis in the work of muscle contraction. It is noted that this energy source was first suggested ninety years ago: that available from ATP is four and a half times smaller than the work done by the surface energy of water in a half-cycle of the red cell glucose transporter (GLUT1). Further, surface energy is a ‘free’ energy source, arising from cycles of water evaporation and condensation within the cells. The mechanical energy effectively comes from the latent heat of condensation of water. Although the latent heat of evaporation comes from thermal energy of the bulk cell-water, itself derived from metabolism, there is no extra hydrolysis of ATP involved. Thus, muscle shortening would be thermally more efficient. If this mechanical concept also applies to cardiac muscle, the increase in efficiency may be vital to medical science as well as to skeletal muscle physiology.