If your question refers to prersonal use, waste reduction, and rain water harvesting are two obvious means.

If it is about larger scale water collection, there are various ways of micro methods like rain water collection ponds to collect run off from a few acres of land in a poly-lined, above-surface mud tanks are available.

Self help methods like low height low tech barrages at frequent intervals built by the villagers along the bank have proved useful in India in restoring dried out rivers to perennial ones, with lot of fish.

Rain harvesting for recharging ground water is another means for raising ground water levels in certain Indian cities, where this was enforced by legislation.