Abstract: Water is stored in a sub-surface reservoir that has flexible walls of grouted in situ soils. The water is stored in the voids between soil particles within the reservoir. Usable voids within the container vary from about 20% to about 40% of the totally enclosed volume of the reservoir. The bottom of the reservoir is a natural impervious sub-strata. No excavating of soil is required as they are, generally, sand and gravel deposits that overlie impervious aquicludes. A grout pipe is inserted into the ground by any conventional method, and then grout is continuously injected through the pipe under pressure as the grout pipe is being withdrawn, thus forcing the grout into adjacent soils. Selective positioning of successive grout pipes leads to the formation of a wall.