Water Harvesting Techniques: Methods and Benefits

Rainfall is unpredictable. In many parts of India and across the developing world, farmers receive most of their annual rain in a few intense months – and then face long dry spells. The challenge isn’t just the total amount of rainfall; it’s that most of it flows away before crops can use it. Water harvesting techniques directly address this problem. By capturing rain where it falls or storing surface runoff in structured reservoirs, these techniques convert erratic rainfall into a dependable resource. They broadly fall into two categories: in situ water harvesting, which retains rainwater at the point where it lands, and surface water harvesting, which collects and stores runoff for later use.

In situ water harvesting 🔗

In situ water harvesting focuses on increasing the amount of rainwater that infiltrates the soil at or near where it falls, rather than letting it drain away as surface runoff. According to the FAO, methods like contour bunds, contour trenches, and vegetative barriers not only intercept runoff but also reduce soil erosion and promote groundwater recharge. These techniques are especially valuable in rainfed farming, where there is no supplemental irrigation to fall back on.

Contour bunding 🔗

Contour bunding involves constructing small earthen embankments along the contour lines of sloping land – lines of equal elevation. When rainfall flows downhill, these bunds interrupt its movement and create temporary storage zones where water can slowly soak into the soil. ICIMOD describes contour bunding as a proven sustainable land management practice for marginal, sloping, and hilly land, widely adopted because it is simple to implement, low cost, and makes maximum use of local resources. The bunds are typically spaced 20-50 metres apart depending on slope steepness, and are most effective on gentle slopes of 2-8% in areas with annual rainfall between 400-800 mm. In deep black cotton soils, however, caution is needed – cracks that form during dry periods can allow water to seep through and breach the bund. Beyond water retention, research by ICRISAT and partner organizations found that contour bunding helped retain soil and nutrients, reduce land degradation, and increase crop productivity at study sites in semi-arid Mali.

Bench terracing 🔗

Bench terracing transforms steep slopes into a series of level, step-like platforms cut horizontally into the hillside. Each platform has a slight inward slope to prevent water from draining off, and the vertical faces between terraces are typically reinforced with stone walls or stabilized with vegetation. This technique is suited to slopes of 15-35%, where contour bunding alone would be insufficient. As described by Satavic Farms, by making structures along contour lines, the flow of rainwater is slowed, reducing runoff and soil erosion while allowing groundwater recharge. Beyond water conservation, bench terracing converts previously uncultivable steep land into productive agricultural plots – a significant advantage in hilly regions where flat land is scarce. The trade-off is cost: bench terracing requires considerably more labour and investment than contour bunding, though the long-term benefits for soil retention and crop production are well established.

Contour trenching 🔗

Contour trenching involves excavating continuous ditches along the contour lines of a slope rather than building raised bunds. These trenches – typically 0.5-1 metre deep and 1-2 metres wide – act as linear reservoirs that intercept surface runoff and hold it until it infiltrates the surrounding soil. According to ScienceDirect, contour trenching is classified as an in situ water harvesting method alongside contour bunds and vegetative barriers, and is particularly effective in areas with high rainfall intensity. Farmers often pair contour trenching with tree planting to create agroforestry systems that benefit from the improved soil moisture. One important maintenance requirement: trenches accumulate sediment over time and need periodic de-silting to maintain their water storage capacity.

Nala bunding 🔗

Nala bunding works with natural drainage channels – locally called nalas – rather than on open field slopes. Nalas are seasonal waterways that carry water during the monsoon but remain dry for most of the year. By constructing a series of low barriers across these channels using stone, earth, or vegetation, nala bunding creates a chain of small temporary reservoirs. Water held behind each bund has more time to infiltrate the surrounding soil and recharge groundwater. An additional benefit is flood moderation: during heavy rainfall, nala bunds slow the peak flow of water, reducing the risk of downstream flooding. They are best suited to undulating landscapes with clearly defined seasonal streams, making them a natural complement to contour bunding on the adjacent agricultural land.

Contour vegetative barriers 🔗

Contour vegetative barriers replace engineered earthen structures with living plant strips. Rows of deep-rooted grasses – vetiver grass being one of the most widely used – or shrubs are planted along contour lines to slow water movement and trap sediment. The International Institute of Tropical Agriculture (IITA) notes that planting trees on top of or along bunds permanently marks and reinforces them, improves soil fertility, and can provide quality forage for livestock when agroforestry species are used. Over time, sediment accumulates on the uphill side of these barriers, naturally building small terraces without any earthmoving. The upfront cost is lower than physical structures, but establishing effective barriers takes time, and the technique works best when combined with other in situ methods.

Surface water harvesting 🔗

While in situ methods retain water on the spot, surface water harvesting takes a different approach: it collects runoff from larger areas and stores it in purpose-built structures for use when rainfall is absent. These structures serve multiple functions – supplying water for irrigation, providing drinking water for livestock, and recharging groundwater aquifers. A comprehensive review published in the journal Water (MDPI, 2025) classifies structures like farm ponds, check dams, percolation tanks, and irrigation tanks as long-term water harvesting structures, designed to bridge the gap between the rainy season and crop water demand throughout the year.

Ponds and tanks 🔗

Farm ponds are small reservoirs, either excavated or formed by constructing an embankment across a low-lying area, that collect and store surface runoff. They are typically constructed on impermeable beds or lined with materials like high-density polyethylene (HDPE) to minimize seepage. Stored water is primarily used for supplemental irrigation, which can significantly reduce crop water stress during dry spells between rainfall events. Farm ponds also provide water for livestock and can support aquaculture, adding an additional income stream. FAO recommends constructing farm ponds for every 4-5 hectares in a watershed to provide protective supplemental irrigation, emphasizing their role in an integrated watershed management approach. One limitation worth noting: farm ponds reduce the volume of water flowing to downstream tanks and ponds, which must be factored into planning.

Storage tanks and reservoirs operate on the same principle at a larger scale – collecting runoff from extended catchment areas and holding it for irrigation or domestic use across wider farming communities. Traditional tank irrigation systems, found extensively across peninsular India, have sustained agriculture in semi-arid regions for centuries. These community-managed systems remain relevant today and form the foundation of many watershed development programmes.

Percolation tanks 🔗

Percolation tanks are a distinct and important category. Unlike farm ponds, which are designed to store water on the surface, percolation tanks are specifically engineered to allow collected runoff to seep into the ground – their primary purpose is groundwater recharge rather than direct water supply. As defined by Chaitanya Rain Harvest Products, a percolation tank is an artificial reservoir constructed across a stream, submerging land with adequate permeability to allow surface runoff to percolate into the groundwater table. They are typically built over second or third order streams, with a storage capacity of 0.1 to 0.5 MCM and a ponded water depth of 3-4.5 metres. The ideal site has highly fractured and weathered rock in the tank bed, which speeds up recharge. Over time, this raises the local groundwater table, benefiting surrounding wells and bore wells and sustaining water availability well beyond the monsoon season. Maharashtra alone has constructed over 10,000 percolation tanks to address groundwater depletion in its agricultural districts.

The long-term value of percolation tanks extends beyond water quantity. As water moves through soil and rock layers, it undergoes natural filtration, improving groundwater quality. Modern project planning now uses Geographic Information Systems (GIS) and remote sensing to identify optimal locations for these structures and monitor their performance – combining traditional techniques with contemporary technology.

Choosing the right technique 🔗

No single water harvesting method suits every situation. The choice depends on a combination of factors: slope gradient, soil type, rainfall pattern, catchment size, and available resources. Gentle slopes (2-8%) favour contour bunding; steeper terrain (15-35%) calls for bench terracing. Sandy soils with high infiltration rates respond well to in situ methods, while clayey soils with low permeability are better suited to surface storage structures. Areas with intense, short-duration rainfall benefit from robust surface collection systems, whereas regions with more gradual rainfall can rely more on in situ infiltration techniques.

In practice, the most effective water management approaches combine multiple techniques. IITA’s technology catalogue highlights that contour bunds work best when integrated with other sustainable agriculture practices such as agroforestry and farmer-managed natural regeneration. Similarly, percolation tanks work synergistically with check dams, farm ponds, and contour bunding to create a layered system of water security across an entire watershed. What all these techniques share is a common goal: slowing water down, giving it time to infiltrate or be stored, and making it available when crops need it most.

What do you think? Given your local rainfall pattern and soil type, which combination of in situ and surface water harvesting techniques do you think would be most practical for the farmers in your region? And as groundwater depletion becomes a growing concern, how important is it to prioritise structures like percolation tanks that focus on recharge rather than just storage?

References

1. https://www.fao.org/4/w7314e/w7314e0q.htm
2. https://www.icimod.org/solutions/contour-bunding/
3. https://archive.iwmi.org/wle/thrive/2020/08/28/how-contour-bunding-and-other-technologies-can-reduce-soil-erosion-and-raise/
4. https://satavic.org/water-harvesting-and-soil-conservation/
5. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/contour-farming
6. https://propas.iita.org/en/solutions/contour-bunds-for-water-harvesting/115/details/
7. https://www.mdpi.com/2073-4441/17/7/976
8. https://www.chaitanyaproducts.com/blog/percolation-tanks-a-component-for-ground-water-recharging/
9. https://e-catalogs.taat-africa.org/com/technologies/contour-bunding-technique-cbt-contour-bunds-for-water-harvesting