Return waters are those flowing from the areas of irrigation systems. Those are composed of field waste waters, viz. surface runoffs, and drainage waters, viz. subsurface waters. Return waters are those returned in an orderly manner from the economic sector of the water cycle to the natural sector (ocean, lakes, lithogenous) by means of technical structures and facilities.

Waste water is irrigation and flushing water drained, respectively, from irrigated agricultural lands and developed areas when cleaning them. Unlike drainage water (groundwater runoff), waste water is formed by surface waters. Waste waters include: 1) waste water from irrigated areas, in particular rice fields; 2) water from irrigation network discharged through outlet ditches in the case of need to immediately stop or reduce water supply.

Drainage waters include: 1) water filtered from canals and irrigation areas, which are pinch out to land surface at backland relief features; 2) water discharged by drainage network.

Return water volume is the difference between the quantity of water consumed by industrial and agricultural enterprises as well as by public utilities and the quantity of water used for production and lost to evaporation.

The chemical composition of return water is determined by the process of salt dissolving and leaching out of the soil and strata of irrigated lands and applied mineral and organic fertilizers or in the result of using technologies of industrial and public utilities, etc. If according to their chemical composition, return water do not cause salinization, it will be reused for irrigation.

Large quantity of return water indicates poor performance of the system. Efficient system operation, loss control in canals, use of proper water application rates, efficiency irrigation method, scheduled water use – all of these allow greatly reducing the quantity of return water.