Rainwater Harvesting

With the water table falling rapidly in most parts of the world, and with concrete buildings, paved car parks, business complexes, and landfill dumps taking the place of water bodies, Rainwater Harvesting is the most reliable solution for augmenting groundwater level. It is the means to attaining self-sufficiency in public distribution of water in drought-prone areas.

Rainwater Harvesting is a cost-effective method of obtaining water, thereby solving the water crisis. It saves the investor more money than what he or she has hitherto spent on water.

Rainwater Harvesting is a cost-effective method of obtaining water, thereby solving the water crisis. It saves the investor more money than what he or she has hitherto spent on water.

Rainwater Harvesting is neither energy-intensive nor labour-intensive, thus making it an eminently feasible alternative to other water-accruing methods, such as desalination of seawater and interlinking of rivers. Rainwater Harvesting is, of course, feasible in regions that receive moderate to heavy rainfall.

For an average rainfall of 1,000mm, approximately four million litres of rainwater can be collected in a year in one acre of land (4047m2), post-evaporation.

Water from rainfall infiltrates into an aquifer through an artificial recharge structure, thus recharging the aquifer. The water is stored in the aquifer, from where it can be retrieved for future use.

Rainwater Harvesting can be undertaken through a variety of ways…
· Capturing run-off from rooftops
· Capturing run-off from local catchments
· Capturing seasonal floodwaters from local streams
· Conserving water through watershed management

These techniques can serve the following purposes:
· Provide drinking water
· Provide irrigation water
· Increase groundwater recharge
· Reduce storm water discharge, urban floods and overloading of sewage treatment plants
· Reduce seawater ingress in coastal areas

In general, Rainwater Harvesting is the activity of direct collection of rainwater. The rainwater collected can be stored for direct use or can be recharged into the groundwater.

Why Rainwater Harvesting?
Water scarcity is a serious problem throughout the world for urban and rural communities. With a burgeoning population, more and more water is required for domestic, industrial and agricultural purposes. In most communities, the rate of withdrawal is far in excess of the rate of recharging the water table.
Urbanization has led to overexploitation of groundwater reserves, reduction in open soil surface and water infiltration rate, and a resultant deterioration in water quality. Apartments and industrial units face acute water shortage, forcing them to spend considerable amounts of money for purchasing water from municipal and private water suppliers.
Water covers about three-fourth of the earth's surface, but only about two per cent is fresh water. Of this small percentage, a large portion is trapped in the polar region.
In Asia, 86 per cent of the fresh water is used for agriculture, eight per cent for industry and six per cent for domestic purposes.
Fresh water, once considered an inexhaustible resource, is now fast becoming a scarce commodity. The main source of freshwater is precipitation, in the form of rain or snow.
When it rains, only a fraction of the water percolates and reaches aquifers; the major portion of rainwater drains out as run-off and goes unused into the ocean.
Further, lack of adequate storage facilities necessitate the procedure of letting rainwater into the sea to prevent breaching and flooding.
The problem is compounded by a burgeoning and over-consumptive population, which has led to a spurt in bore-wells and also an increase in depth of bore-wells. The two phenomena are manifestations of over-pumping of groundwater reserves. The unrestricted use of bore-wells threatens groundwater resources.
The problem of groundwater depletion in cities and elsewhere can be best tackled by harnessing every drop of rainwater for the purpose of artificial recharge of the water table.

The main objectives of Rainwater Harvesting are:
· To conserve surface run-off during monsoons.
· To recharge aquifers and increase availability of groundwater
· To improve the quality of groundwater, where required
· To overcome the problem of flooding and stagnation of water during monsoon season
· To arrest sea-water intrusion

Artificial Recharge

Necessity And Purpose

"Artificial Recharge" may be defined as the practice of increasing by artificial means the amount of water that enters into an aquifer. This is accomplished by augmenting the natural infiltration of precipitation or surface water into underground formations by employing appropriate systems and techniques.

The demand for potable water is increasing day by day, resulting in extraction of more and more groundwater. Such extraction is far in excess of net average recharge from natural sources; hence, it is necessary to artificially recharge aquifers to balance the output.

The quantity of seepage depends upon soil conditions. The percolated water joins aquifers and this percolation contributes enormously to the building of the ground water table. As mentioned earlier, Artificial Recharge is the process of augmenting the underground water table by artificial infiltration of rainwater and surface run-off.

Various methods are available to recharge the water table by increasing the rate of infiltration. Artificial Recharge can be achieved by:
1) Obstructing the flow of water
2) Storing the water
3) Spreading the water
4) Injecting it through wells and bore wells.

1) Creates a groundwater ridge or mound around existing groundwater extraction structures.
2) Minimizes the depth of water to pumping level.
3) Minimizes the cone of depression, cost and duration of pumping.
4) Increases discharge rates.
5) Improves quality of groundwater in terms of total dissolved solids.
6) Increases annual groundwater recharge.
7) Prevents temporal decline of water table in the region.
8) Creates a scope for additional groundwater extraction.
9) Maintains a safe groundwater balance.
10) Improves the overall available groundwater potential in the area.
11) Prevents salinity intrusion.
12) Prevents mutual interference between ground water extraction structures.

Roof Water Harvesting

Rooftops of houses are excellent collection centres for rainwater. If properly diverted from rooftops and used for artificial recharge, rainwater will augment the groundwater table to a sufficient extent

In Roofwater Harvesting, the roof is connected to the well through a network of pipes and filtering system

Rainwater that lands on roofs and elevated platforms is likely to be contaminated by foreign elements, such as dust, leaves and bird droppings. These foreign elements can be prevented from entering the well by flushing

off the initial water flowing through the pipes at the beginning of rainfall. A gate valve system can be used for this purpose. The valve system is effective. It is a scientific fact that only the first 10mm of rainwater carries impurities. It is, thus, this amount that needs to be discarded; the rest is comparatively free from foreign elements. For filtering roof water for the purpose of diverting roof water to wells, KRG models 1 or 2 may be used. The roof water can be subsequently directed to the well, preferably through a filtering tank containing filter media like pebbles and sand.

Air introduced into a well during diverting of water from the roof may affect the infiltration of water. Air bubbles tend to occupy the space in the interstices, thereby reducing effective porosity, which blocks the movement of roof water into the well. The formation of air bubbles can be avoided by lowering the inlet pipe below the static water level.

Rainwater Collection for Drinking Purpose

Two types of Rainwater Harvesting schemes can be designed and constructed for collection of rainwater for drinking.

a) Domestic Rainwater Collection

In the scheme, the rainwater collected from roofs, courtyards and small catchment platforms can be stored in concrete sumps, Ferro Cement tanks or High Densile Polythene (HDP) tanks.

b) Community Rainwater Collection

In community schemes, the rainwater collected from the roofs of a number of buildings may be led into a large-size underground tank or to a nearby pond. If the water is diverted to ponds, located on hydrologically favourable zones, a production well can be constructed on the downstream side of the pond to tap the water for drinking purposes.

Surface Water Harvesting

Artificial Recharge Structures

Percolation Pit

To directly divert rainwater into an aquifer, a percolation pit is made. This structure is covered with a perforated concrete slab.

Whenever the depth of clay soil is more, recharge through a percolation pit with bore is preferable. This bore can be at the centre of the pit, which is filled with pebbles. The top portion is filled with river sand. The pit itself is covered with a perforated concrete slab. Depending on the lithology, necessary casing has to be provided in the recharge shaft to avoid clogging
Roof water and surface water from buildings can be diverted to percolation pits. It is advisable to have at least one percolation pit in every house with open area for every 20 square metres

Dug Cum Bore Well (DCB)

DCB is a type of percolation pit with a large chamber and deeper inwell bore. If necessary, more than one shaft is installed in the same recharge well. Conventional filter media is used to filter the recharge water. Coir packing can also be provided to achieve maximum efficiency in filtering the recharge water. If the area is prone to flooding, it is advisable to provide necessary air vent to the DCB to avoid air locking.

Trench cum Percolation Pit (TCP)

TCP is one of the most ideal recharge structures in limited open land, narrow streets and roads to trap surface water and recharge the aquifer. One or two suitable shafts can also be provided inside the trench, depending on the subsurface formation and depending on the availability of water for recharge purpose. The entire structure may be filled with pebbles or locally available boulders and sand. If necessary, the structure can be covered with perforated slabs.

TCP can be located on roadsides; street corners; low-lying areas inside the premises of individual houses; multi-storey buildings; paved areas surrounding a house; and near water-extraction structures, like hand pumps, bore wells and dug wells.

Mini Artificial Aquifer System (MAAS)

MAAS is a unique artificial recharge structure, which is ideally suitable for open areas, particularly low-lying areas. Besides open areas, this structure is suitable for junctions of roads; street corners; parks; stadiums; playgrounds; bus terminuses; theatres; and open areas of public buildings, schools and colleges.

In open areas, the topsoil and clay portion of the subsurface should be excavated. The excavated portion may be filled with locally available boulders of various sizes of ascending order from the top. The top portion may be filled with coarse river sand.

Preservation of Run-Off Water

The ground level near the gate of a house, say, should be raised to retain as much water as possible inside the compound. It is recommended to construct a sloping gutter across the gate and direct the rushing water towards a Rainwater Harvesting structure. For multi-storied buildings, it is advisable to direct the water to a recharge well.

Artificial Recharge in Roads and Colonies

An enormous quantity of surface water generated during monsoon, flows through paved roads, particularly concrete surfaces, of residential colonies. This precious water can be diverted to site-specific recharge structures on the roads. All the water-extracting structures of colonies, particularly bore wells and hand pumps of houses on either side of roads, are bound to give sustainable yield in due course of time.

Recharging through Defunct open wells, bore wells and hand pumps

Due to severe depletion of ground water table, many open wells, bore wells and hand pumps are getting dried up. Instead of discarding them, it is advisable to convert them into useful recharge structures. Roof water and run-off water can be diverted into these structures, after filling them with pebbles and river sand. An effective arrangement should be made for desilting before diverting the water into these structures.

Rainwater Harvesting through Ponds

Rainwater collected from the roofs of houses may be led into nearby ponds (with pervious top layer) through pipelines for recharging groundwater aquifers. Run-off water can also be diverted to the ponds, after making proper desilting arrangements. A production well can be constructed, nearby, to tap the water recharged.

Rainwater Harvesting Through Ditch and Furrow System

The Ditch and Furrow system can be designed to suit the topographic and geological conditions that exist at a potential artificial recharge site. The system is particularly effective in cases where recharge water contains high loads of suspended sediments.

The segment on the side of the road should be covered with a perforated slab. It should have percolation pits of depths ranging from 20 feet to 50 feet at regular intervals, depending on the soil conditions.

Artificial Recharge in Farms and Irrigation Lands

It is advisable to have numerous percolation pits in agricultural lands for gradual percolation and recharging of aquifers. Construction of small bunds on sloping areas slows down run-off water and helps in easy percolation. Run-off water can be diverted into a large well through a Baby well and filtering tank to avoid silt depositing in the well.
Depending on the terrain, geology and gradient, different methods are adopted in farms and irrigation lands. This manoeuvre involves storing, spreading, percolating and blocking.
In gradient land, construction of bunds will slow down run-off water, enabling stagnation and slow percolation. In areas containing deep slopes, it is advisable to dig trenches and a series of ponds. In this method, water is stored in ponds; any overflowing water spreads and percolates, saturating the entire area.
In plain flat terrain, storing ponds are built along with canals, which have trenches. Recharging wells are built in between, with proper desilting arrangements.
In rocky region, a thorough study must be made to locate potential aquifers. Infiltration is possible to enhance quantity of water in aquifers by means of recharge wells.
In totally dry land, Sieve Plantation is adopted to convert it into a fertile land. Pitting, bunding and planting are executed together in this system.
On riverbeds, construction of Bandharas helps enhance recharging. Bandharas are concrete walls on impermeable soil, built across the river but below the riverbed, at regular intervals. These could act as underground reservoirs, which recharge the surrounding area.
By extension, wastewater in the region can be treated and let off to the river, so that it will recharge the aquifer and, thus, help farmers and dwellers on the banks of the river.

Sewerage treatment

Biological treatment

In this treatment system, 'Actizyme pellets', which contain safe and harmless bacteria, are added to sewage water. The bacteria will multiply prodigiously and eat suspended solids and harmful bacteria.

This type of treatment will improve and accelerate biological degradation of organic wastes by microbial augmentation, with particular emphasis on reducing odours and lowering pollution levels (example: Biological Oxygen Demand (BOD) and suspended solids). Usage of this biological treatment is recommended in all types of systems, including sewage treatment plants, rice mills, pumping stations, oxidation ponds, lagoons, trickling filters, anaerobic digesters, package plants and septic tanks.

The distinct benefits of this process are:
1) Reduced odours (including sulphide).
2) Reduced BOD levels.
3) Reduced turbidity and suspended solids.
4) Reduced ammonia and nitrogen levels.
5) Reduced grease and fat levels.
6) Reduced sludge levels.

Actizyme usage is usually through an initial shock dosage to clean and condition the system. This is followed by a maintenance dosing on a regular basis to enable the beneficial microorganisms to establish their population. This situation may facilitate the bacteria to bloom frequently and to replace natural losses in the system.

Dosage rates vary from system to system, which depends on hydraulic and organic loads. However, for domestic sewerage dosage, it can be as low as 0.5 ppm of hydraulic loading.

The specific 'Actizyme' product used will depend on the circumstances. It is strongly recommended that advice be sought from a trained technical adviser. Actizyme is safe to use - no special precaution is necessary for handling.

These pellets are approved by the Ministry of Environment and Forest, New Delhi. SGS (India) Ltd has already accepted them, after conducting a Non-Toxic Test.

Grey water treatment

Reed Bed System

This aerobic biological grey water treatment process uses the reed 'Phragmites'. The reeds keep the bed of soil or gravel partially aerobic by pumping atmospheric oxygen down to their roots. Microorganisms in the soil carry out the purification processes.

A bed of rhizomes of the reed phragmites provides a hydraulic pathway through which the wastewater flows. This pathway (rhizosphere) in the movement of the mesh of roots, rhizomes and soil prevents clogging of the rhizosphere. The reeds provide atmospheric oxygen to the rhizosphere via the leaves, stems, roots and rhizomes. Wastewater is, therefore, treated aerobically by bacterial activity in the rhizosphere and also anaerobically in the surrounding soil.

In addition to treating grey water, it is possible to compost sludge aerobically above ground level in a layer of straw, derived from the dead leaves and stems of the reeds.

The method involves the construction of a trench of 1.5 metres depth, below the depth of grey water flow. The trench should be sealed with clay, synthetic fabric or asphalt to retain water and to prevent contamination of groundwater. After sealing the bottom of the trench, the soil in which the reeds are to be planted is placed in the trench. The trench is filled with river sand and lime powder, which is to be added to the extent of two to 2.5 kilograms.

The inlet and outlet ends of the bed are provided with another suitable trench, filled with pebbles, boulders or granite, which act as a filtering media. The outlet is via a pipe, whose level can be varied, so that the water level in the bed can be raised or lowered. For the successful growth of Phragmites, it is essential for the soil to remain waterlogged, but not necessarily covered with water, for most of the year.

A mature reed transpires and evaporates about 1500mm of water annually. Therefore, it is important to have an adequate supply of water usually after the reeds are planted in a new bed. It takes about three years before the bed matures sufficiently to become operational. In the initial phase, fresh water is supplied to the bed, but as time passes by and the reeds become established, grey water can be added in increasing levels of concentration. After three years, grey water can be added without dilution.

Reed beds are simple and cheap to form, operate and maintain while giving a consistent effluent quantity over a wide range of conditions. They are eco-friendly, since they merge with the surrounding environment. "Canna indica " is an ideal plant.

The Reed Bed system can also be applied to recycle wash water (bathing and hand wash water) from residences and office buildings.

Reed bed system for individual houses and multi-storey buildings

Bathing water can be diverted to a trench, constructed adjacent to the compound wall. 'Canna indica' can be grown in the trench. A few percolation pits or recharge wells can be constructed at the outlet side of the trench. This will solve the problem of stagnation of domestic discharge and also improve the quality and quantity of water in the aquifer.

Recycling And Treating

For every 100 litres of water required per capita per day, the consumption is approximately as follows:

15 litres for cooking and drinking
55 litres for washing and bathing
30 litres for flushing the toilet

Recycling the wash and bath water and using it for toilet flushing can save 30 per cent of the precious drinking water.

Even during the breakdown of monsoon, the consumption of water and consequent domestic discharge is not reduced. These factors necessitate the treatment of huge quantity of domestic discharge by cost effective methods, where the treated water can be subsequently used for irrigation and recharge purposes.

Mineral Water Bottle Irrigation Method

This is a simple and effective system for watering newly planted saplings. Insert two or three cotton wicks at the bottom of a mineral water bottle. Replace the existing topsoil with river sand and, then, plant the bottle below ground level in the vicinity of the sapling.

In this system, water poured in the bottle will remain for more than a week, as it will only trickle out, through the cotton wicks. Thanks to the system, the moisture content in the soil is maintained, thereby benefiting the roots of the plant in a sustained manner. The system is beneficial from a conservation point of view, because it supplies only that much water that is needed by the plant.