Rain Water Harvesting methods

All living things including, plants, animals and human beings need water to live and to carry out different cellular activities.

Have you ever imagined a day without water?  

No, we have not and it is hard to imagine. We all use water for different kinds of day to day activities, such as cleaning, washing, bathing, cooking, drinking and other domestic and industrial uses.

Water is a precious, essential and abiotic component of the ecosystem. Today we all are heading toward the scarcity of water, and this is mainly because of the lack of water conservation and pollution of water bodies. So, let us not waste a drop of water and start conserving water for further use.

Also read: Water

There are different methods used for conserving water, here let us learn about the rainwater harvesting system.

What is Rainwater harvesting?

Rainwater harvesting is the simple process or technology used to conserve Rainwater by collecting, storing, conveying and purifying of Rainwater that runs off from rooftops, parks, roads, open grounds, etc. for later use.

How to Harvest the Rainwater?

Rainwater harvesting systems consists of the following components:

Catchment- Used to collect and store the captured Rainwater.

Conveyance system – It is used to transport the harvested water from the catchment to the recharge zone.

Flush- It is used to flush out the first spell of rain.

Filter – Used for filtering the collected Rainwater and remove pollutants.

Tanks and the recharge structures: Used to store the filtered water which is ready to use.

The process of rainwater harvesting involves the collection and storage of rainwater with the help of artificially designed systems that run off naturally or man-made catchment areas like- the rooftop, compounds, rock surface, hill slopes, artificially repaired impervious or semi-pervious land surface.

Several factors play a vital role in the amount of water harvested. Some of these factors are:

The quantum of runoff

Features of the catchments

Impact on the environment

Availability of the technology

The capacity of the storage tanks

Types of the roof, its slope and its materials

The frequency,  quantity  and the quality of the rainfall

The speed and ease with which the Rainwater penetrates through the subsoil to recharge the groundwater.

Why do we Harvest Rainwater?

The rainwater harvesting system is one of the best methods practised and followed to support the conservation of water. Today, scarcity of good quality water has become a significant cause of concern. However, Rainwater, which is pure and of good quality, can be used for irrigation, washing, cleaning, bathing, cooking and also for other livestock requirements.

Advantages of Rainwater Harvesting

The benefits of rainwater harvesting system are listed below.

Less cost.

Helps in reducing the water bill.

Decreases the demand for water.

Reduces the need for imported water.

Promotes both water and energy conservation.

Improves the quality and quantity of groundwater.

Does not require a filtration system for landscape irrigation.

This technology is relatively simple, easy to install and operate.

It reduces soil erosion, stormwater runoff, flooding, and pollution of surface water with fertilizers, pesticides, metals and other sediments.

It is an excellent source of water for landscape irrigation with no chemicals and dissolved salts and free from all minerals.

Also Read: Disappearing Act of Water

Disadvantages of Rainwater Harvesting

In addition to the great advantages, the rainwater harvesting system has a few disadvantages like unpredictable rainfall, unavailability of the proper storage system, etc.

Listed below are few more disadvantages of the rainwater harvesting process.

Regular Maintenance is required.

Requires some technical skills for installation.

Limited and no rainfall can limit the supply of Rainwater.

If not installed correctly, it may attract mosquitoes and other waterborne diseases.

One of the significant drawbacks of the rainwater harvesting system is storage limits.

Know more about Rainwater Harvesting and other Biology related concepts at BYJU’S Biology

What are the different methods of rainwater harvesting?

The different methods of rainwater harvesting include:

Rooftop rainwater harvesting.

Surface runoff harvesting.

First, flush.

Transportation.

Catchment.

Filter.

What is the importance of rainwater harvesting?

Rainwater harvesting is a sustainable process that helps in preserving water for future needs. Water scarcity is a major concern in today’s scenario. The process of rainwater harvesting is a good way to conserve water.

What are the advantages of rainwater harvesting?

The advantages of rainwater harvesting are:

It is cost-effective

Conserves water

A source of water for landscape irrigation

It is a simple method and easy to practice

It reduces soil erosion and pollution of water bodies due to fertilizers and pesticides

What are the factors affecting the amount of rainwater harvested?

The factors affecting the amount of rainwater harvested are:

Catchment features

Quantum of runoff

The capacity of storage tanks

Methods of Rainwater Harvesting

1. Surface Runoff Harvesting

In urban areas, rainwater flows away as surface runoff. This runoff can be caught and used for recharging aquifers by adopting appropriate methods.

2. Rooftop Rainwater Harvesting

It is a system of catching rainwater where it falls. In rooftop harvesting, the roof becomes the catchment, and the rainwater is collected from the roof of the house/building.

It can either be stored in a tank or diverted to an artificial recharge system. This method is less expensive and very useful and, if implemented correctly, helps in augmenting the groundwater level of the area.

Components of the Rooftop Rainwater Harvesting

The illustrative design of the essential components of the rooftop rainwater harvesting system is given in the typical schematic diagram . The system mainly constitutes of following sub-components:

1. Catchment

The surface that receives rainfall directly is the catchment of rainwater harvesting system. It may be a terrace, courtyard, or paved or unpaved open ground.

The terrace may be a flat RCC/stone roof or sloping roof. Therefore the catchment is the area, which actually contributes rainwater to the harvesting system.

2. Transportation

Rainwater from the rooftop should be carried through down to take water pipes or drains to the storage/harvesting system. Water pipes should be UV resistant (ISI HDPE/PVC pipes) of the required capacity.

Water from sloping roofs could be caught through gutters and down take the pipe. At terraces, the mouth of each drain should have wire mesh to restrict floating material.

3. First Flush

The first flush is a device used to flush off the water received in the first shower. The first shower of rains needs to be flushed-off to avoid contaminating storable/rechargeable water by the probable contaminants of the atmosphere and the catchment roof.

It will also help in cleaning of silt and other material deposited on the roof during dry seasons. Provisions of first rain separators should be made at the outlet of each drainpipe.

4. Filter

There is always some skepticism regarding Roof Top Rainwater Harvesting since doubts are raised that rainwater may contaminate groundwater. There is a remote possibility of this fear coming true if the proper filter mechanism is not adopted.

Secondly, all care must be taken to see that underground sewer drains are not punctured, and no leakage is taking place in close vicinity.

Filters are used for the treatment of water to effectively remove turbidity, color, and microorganisms. After the first flushing of rainfall, water should pass through filters.

A gravel, sand, and ‘netlon’ mesh filter is designed and placed on top of the storage tank. This filter is very important in keeping the rainwater in the storage tank clean. It removes silt, dust, leaves, and other organic matter from entering the storage tank.

The filter media should be cleaned daily after every rainfall event. Clogged filters prevent rainwater from easily entering the storage tank and the filter may overflow. The sand or gravel media should be taken out and washed before it is replaced in the filter. 

There are different types of filters in practice, but the basic function is to purify water. Different types of filters are described in the following section:

1. Sand Gravel Filter

These are commonly used filters, constructed by brick masonry and filleted by pebbles, gravel, and sand. Each layer should be separated by wire mesh.

2. Charcoal Filter

Charcoal filters can be made in-situ or in a drum. Pebbles, gravel, sand, and charcoal as shown in the figure should fill the drum or chamber. Each layer should be separated by wire mesh. The thin layer of charcoal is used to absorb odor if any.

3. PVC –Pipe filter

This filter can be made by PVC pipe of 1 to 1.20 m length; Diameter of pipe depends on the area of roof. Six inches dia. pipe is enough for a 1500 Sq. Ft. roof and 8 inches dia. pipe should be used for roofs more than 1500 Sq. Ft. Pipe is divided into three compartments by wire mesh.

Each component should be filled with gravel and sand alternatively as shown in the figure. A layer of charcoal could also be inserted between two layers.

Both ends of the filter should have a reduction of the required size to connect the inlet and outlet. This filter could be placed horizontally or vertically in the system. A schematic pipe filter

4. Sponge Filter

It is a simple filter made from PVC drum having a layer of sponge in the middle of drum. It is the easiest and cheapest form filter, suitable for residential units. A typical figure of sponge filter

Methods of Rooftop Rainwater Harvesting

Various methods of using roof top rainwater harvesting are illustrated in this section.

1. Storage of Direct Use

In this method, rainwater collected from the roof of the building is diverted to a storage tank. The storage tank has to be designed according to the water requirements, rainfall, and catchment availability.

Each drainpipe should have a mesh filter at the mouth and first flush device followed by a filtration system before connecting to the storage tank. Each tank should have an excess water overflow system.

Excess water could be diverted to the recharge system. Water from storage tanks can be used for secondary purposes such as washing and gardening etc. This is the most cost-effective way of rainwater harvesting.

The main advantage of collecting and using rainwater during the rainy season is not only to save water from conventional sources but also to save energy incurred on transportation and distribution of water at the doorstep. This also conserves groundwater, if it is being extracted to meet the demand when rains  of a storage tank

2. Recharging Groundwater Aquifers

Groundwater aquifers can be recharged by various kinds of structures to ensure the percolation of rainwater in the ground instead of draining away from the surface. Commonly used recharging methods are:-

Recharging of bore wells

Recharging of dug wells.

Recharge pits

Recharge Trenches

Soakaways or Recharge Shafts

Percolation Tanks

3. Recharging of Bore Wells

Rainwater collected from the rooftop of the building is diverted through drainpipes to settlement or filtration tank. After settlement, filtered water is diverted to bore wells to recharge deep aquifers. Abandoned bore wells can also be used for recharge.

Optimum capacity of the settlement tank/filtration tank can be designed based on the area of catchment, intensity of rainfall, and recharge rate. While recharging, entry of floating matter and silt should be restricted because it may clog the recharge structure.

The first one or two showers should be flushed out through rain separator to avoid contamination. Fig 6 indicates a schematic diagram of a filtration tank recharging to the bore well.

4. Recharge Pits

Recharge pits are small pits of any shape rectangular, square, or circular contracted with brick or stone masonry wall with weep hole at regular intervals. Top of the pit can be covered with perforated covers. The bottom of the pit should be filled with filter media.

The capacity of the pit can be designed based on the catchment area, rainfall intensity, and recharge rate of the soil. Usually, the dimensions of the pit may be of 1 to 2 m width and 2 to 3 m deep, depending on the depth of previous strata.

These pits are suitable for recharging of shallow aquifers, and small houses. A schematic diagram of the recharge pit 

5. Soakway or Recharge Shafts

Soak away, or recharge shafts are provided where the upper layer of soil is alluvial or less porous. These are the bored hole of 30 cm dia. up to 10 to 15 m deep, depending on the depth of the pervious layer. Bore should be lined with slotted/perforated PVC/MS pipe to prevent the collapse of the vertical sides.

At the top of the soakaway, the required size sump is constructed to retain runoff before the filters through the soakaway. Sump should be filled with filter media. A schematic diagram of the recharge shaft

6. Recharge Trenches

The recharge trench is provided where upper impervious layer of soil is shallow. The recharge trench excavated on the ground and refilled with porous media like pebbles, boulders, or brickbats. It is usually made for harvesting the surface runoff.

Bore-wells can also be provided inside the trench as recharge shafts to enhance percolation. The length of the trench is decided as per the amount of runoff expected.

This method is suitable for small houses, playgrounds, parks, and roadside drains. The recharge trench can be of size 0.50 to 1.0 m wide and 1.0 to 1.5 m deep. Fig. 10 presents a schematic diagram of recharging to trenches.

7. Percolation Tank

Percolation tanks are artificially created surface water bodies, submerging a land area with adequate permeability to facilitate sufficient percolation to recharge the groundwater. These can be built on big campuses where land is available, and topography is suitable.

Surface runoff and roof topwater can be diverted to this tank. Water accumulating in the tank percolates in the solid to augment the groundwater.

The stored water can be used directly for gardening and raw use. Percolation tanks should be built in gardens, open spaces, and roadside greenbelts of urban areas.

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