Water harvesting is the collection of runoff for productive purposes. Instead of runoff being left to cause erosion, it is harvested and utilized. In the semiarid droughtprone areas where it is already practised, water harvesting is a directly productive form of soil and water conservation. Both yields and reliability of production can be significantly improved with this method. Water harvesting WH can be considered as a rudimentary form of irrigation. The difference is that with WH the farmer or more usually, the agropastoralist has no control over timing. Runoff can only be harvested when it rains. In regions where crops are entirely rainfed, a reduction of 50 in the seasonal rainfall, for example, may result in a total crop failure. If, however, the available rain can be concentrated on a smaller area, reasonable yields will still be received. Of course in a year of severe drought there may be no runoff to collect, but an efficient water harvesting system will improve plant growth in the majority of years.

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