One of the major environmental benefits of drainage is its positive impact on improving the health of humans, plants and farm animals. Drainage of wet, swampy areas has led to a reduction in mosquito breeding sites in all parts of the world. The effect has been a drop in the incidence and prevalence of important water related and mosquito transmitted diseases, e.g., malaria, yellow fever and filariasis.

Furthermore, drainage of stagnant water can eliminate foot-rot in large animals and, to a certain extent, the breeding environment of aquatic and semi-aquatic snails, which are the intermediate host of schistosomiasis. Drainage also reduces or eliminates mildew infections and various root rots of plants.

By growing high value food crops in well-drained soils, the health, nutrition and economic status of rural populations can be improved. There are also increased opportunities for employment, as new industries may develop in prosperous areas.

Where drainage is used to reclaim salinized and waterlogged lands, it is an environmentally beneficial practice, because the land is returned to its full productive potential. The adaptation of subsurface drainage systems to serve as sub-irrigation or controlled drainage systems leads to other benefits, i.e., the reduction of nitrate pollution.

The field-scale benefits of drainage can be summarized as follows:

1. Drainage promotes beneficial soil bacteria activity and improves soil tilth.
2. There is less surface runoff and soil erosion on drained land.
3. Improved field machine trafficability reduces soil structural damage. Soil compaction is reduced and less energy is required for field machine operations. Drainage also allows for timelier field operations. Consequently, the growing season can be lengthened and crops can achieve full maturity.
4. Crop yields are increased because of improved water management and uptake of plant nutrients.
5. Higher value crops can be planted, and there is flexibility to introduce new and improved cropping systems.
6. In general, land value and productivity are increased.
7. Farm income is increased and income variability reduced.
8. Drainage maintains favourable salt and air environments in the crop root zone.