Prediction of elastic deflection in water tank wall subjected to triangular distributed liquid load using finite difference has been derived in the present study. A good agreement was found through the comparisons between the present model and the Timoshenko and Woinowsky-Krieger based on theory of plates and shells theory. Length to depth ratio of 1, 2, 3 and 4 were taken as a parametric study. An increase of 14.5%, 37.8% and 46.3% were obtained for L/h=2, 3, and 4 compares with L/h=1