Components, Transportation, and Storage of Rainwater Harvesting Methods

Raja Faizan Rasool April 4, 2023

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Table of Contents

Components, Transportation, and Storage of Rainwater Harvesting Methods.

Generally, there are two methods for harvesting rainwater: surface runoff and rooftop rainwater. Rainwater harvesting is the practice of collecting and storing rainwater for on-site reuse rather than letting it run off. The stored water is used for various purposes, including gardening, irrigation, etc. This article discusses multiple rainwater harvesting methods.

Rainwater Harvesting Techniques

1. Surface Runoff Capture

Rainwater drains away as surface runoff in cities. This runoff can be captured and used to recharge aquifers using appropriate methods.

2. Rainwater Harvesting on the Roof

It is a method of collecting rainwater where it falls. The roof becomes the catchment in rooftop harvesting, and rainwater is collected from the top of the house/building.

It can be stored in a tank or diverted to a manufactured recharge system. This method is less expensive and very useful, and if properly implemented, it contributes to increasing the area’s groundwater level.

Rooftop Rainwater Harvesting Components

The typical schematic diagram in Fig 1 depicts the illustrative design of the essential components of the rooftop rainwater harvesting system. The system is made up of the following sub-components.

1)- Capture

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

The terrace roof could be flat RCC/stone or sloping. As a result, the catchment is the area that contributes rainwater to the harvesting system.

2)- Modes of transportation

Rainwater from the rooftop should be carried 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)- The First Flush

The first flush is a device that is used for flushing away the water from the first shower. The first rain shower must be flushed away to avoid contaminating storable/rechargeable water with pollutants from the atmosphere and the catchment roof.

It will also aid in removing silt and other debris from the roof during dry seasons. At the outlet of each drainpipe, first rain separators should be installed.

4)- Use a filter

There is always some skepticism about Roof Top Rainwater Harvesting because there is concern that rainwater will contaminate groundwater. If the proper filter mechanism is not implemented, this fear cannot come true.

Second, all precautions must be taken to ensure that underground sewer drains are not punctured and that no leakage occurs in the immediate vicinity.

Filters effectively remove turbidity, color, and microorganisms from water. Water should be filtered after the initial flushing of rainfall.

On top of the storage tank, a gravel, sand, and ‘nation’ mesh filter is designed and installed. This filter is critical for keeping rainwater clean in the storage tank. It keeps silt, dust, leaves, and other organic matter from the tank.

After each rainfall event, the filter media should be cleaned daily. Clogged filters make it difficult for rainwater to enter the storage tank, and the filter may overflow. Before replacing the sand or gravel media in the filter, it should be removed and washed. Figure 2 depicts a typical filter photograph.

CapturePhotograph of Typical Filter in Rainwater Harvesting

Filters come in various shapes and sizes, but they primarily purify water. The sections that follow describe multiple types of filters:

1)- Filter made of sand and gravel

These are standard filters made of brick masonry and filled with pebbles, gravel, and sand. The wire mesh should be used to separate each layer.

2)- Activated Charcoal Filter,

In-situ or drum-made charcoal filters are available. The drum or chamber should be filled with pebbles, gravel, sand, and charcoal, as shown in the figure. The wire mesh should be used to separate each layer. A thin layer of charcoal is used to absorb any odors.

3)- Filter for PVC pipes

This filter can be made out of PVC pipe that is 1 to 1.20 m long; the pipe’s diameter depends on the roof’s area. A top of 1500 square feet requires six inches of line, while tops more oversized than 1500 square feet need eight inches of pipe. Wire mesh divides the tube into three compartments.

As shown in the figure, each component should be filled with gravel and sand alternately. Between two layers, a layer of charcoal could also be inserted.

Both ends of the filter should be reduced in size to connect the inlet and outlet. This filter could be installed in the system horizontally or vertically. Figure 3 depicts a schematic pipe filter.

4)-Sponge Filter

It is a simple filter made of a PVC drum with a sponge layer in the middle. It is the most detailed and most affordable form filter for residential units. Figure 6 depicts a typical sponge filter figure 6.

Rooftop Rainwater Harvesting Methods

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

1. Direct Use Storage

Rainwater collected from the building’s roof is diverted to a storage tank using this method. Water requirements, rainfall, and catchment availability must all be considered when designing the storage tank.

Before connecting to the storage tank, each drainpipe should have a mesh filter at the mouth and a first flush device, followed by a filtration system. An excess water overflow system should be installed in each tank.

Excess water could be used to recharge the system. Water from storage tanks can be used for various purposes, including washing and gardening. This is the most cost-effective method of rainwater collection.

The primary benefit of collecting and using rainwater during the rainy season is that it saves water from not only conventional sources but also energy on the transportation and distribution of water at the door. This also conserves groundwater if extracted to meet demand during rainy seasons. Figure 5 depicts a typical storage tank diagram.

A storage tank on a platform painted white

2)- Groundwater Aquifer Recharge

Groundwater aquifers can be recharged by various structures that ensure rainwater percolates into the ground rather than draining away from the surface. The following are standard recharge methods:

Recharging boreholes
Well refilling.
Pits for recharging
Trenches Recharge
Shafts of Recharge or Soakaways
Tanks for Percolation

3)- Bore Well Recharging

Rainwater collected from the building’s roof is routed through drainpipes to a settlement or filtration tank. Filtered water is diverted to bore wells after payment to recharge deep aquifers. Bore wells that have been abandoned can also be used for recharge.

The settlement tank/filtration tank’s capacity can be optimized based on the catchment area, rainfall intensity, and recharge rate. Floating matter and silt should be kept out of the recharge structure because they can clog it.

The first one or two showers should be flushed out through a rain separator to avoid contamination. Figure 6 depicts a schematic diagram of a filtration tank that is recharging to a bore well.

CaptureFiltration Tank Recharging to Bore Well

4)-Recharge Pits

Recharge pits are small pits of any shape that are contracted with a brick or stone masonry wall and have weep holes at regular intervals. Perforated covers can be used to cover the pit’s top. Filter media should be placed in the pit’s bottom.

The capacity of the pit can be calculated using the catchment area, rainfall intensity, and soil recharge rate. The pit’s dimensions are typically 1 to 2 m wide and 2 to 3 m deep, depending on the depth of the previous strata.

These pits are ideal for recharging shallow aquifers and building tiny houses. Figure 7 depicts a schematic diagram of the recharge pit.

5)- Recharge Shafts or Soakaways

Where the upper layer of soil is alluvial or less porous, soak-away or recharge shafts are provided. These are bored holes with a diameter of 30 cm and a depth of 10 to 15 m, depending on the depth of the previous layer. The bore should be lined with slotted/perforated PVC/MS pipe to prevent the vertical sides from collapsing.

The required size sump is built at the top of the soakaway to catch runoff before it filters through the soakaway. Filter media should be placed in the sump. Figure 8 depicts a schematic diagram of the recharge shaft.

6)- Dug Well Recharging

Wells that have been dug can be used as a recharge structure. After passing through the filtration bed, rainwater from the roof is diverted to drilled wells. Cleaning and desalting of dug wells should be done regularly to improve the recharge rate. For bore well recharging, the filtration method suggested could be used. Figure 9 depicts a schematic diagram of renewing a dug well.

Schematic Diagram of Recharging to Dug Well

7)- Trenches Recharge

Where the upper impervious layer of soil is shallow, a recharge trench is provided. The recharge trench was excavated and refilled with porous media such as pebbles, boulders, or brickbats. It is typically designed to collect surface runoff.

Bore wells can also be installed as recharge shafts inside the trench to improve percolation. The length of the track is determined by the amount of runoff anticipated.

This method is appropriate for small dwellings, playgrounds, parks, and roadside drains. The recharge trench can range in width from 0.50 to 1.0 m and depth from 1.0 to 1.5 m. Figure 10 depicts a schematic diagram of trench recharging.

8)- Tank for Percolation

Percolation tanks are artificial surface water bodies that submerge a land area with enough permeability to allow sufficient percolation to recharge the groundwater. These can be built on large campuses with enough land and suitable topography.

This tank can be used to collect surface runoff and roof topwater. Water from the tank percolates into the solid, supplementing groundwater.

The water that has been stored can be used directly for gardening and other purposes. Percolation tanks should be installed in urban gardens, open spaces, and roadside greenbelts.

FAQs on Rainwater Harvesting Methods? What are the methods for collecting rainwater?

There are two methods for collecting rainwater: surface runoff collection and rooftop rainwater collection.

What exactly is rainwater harvesting?

Rainwater harvesting is the practice of collecting and storing rainwater for on-site reuse rather than letting it run off. These stored waters are used for various purposes, including gardening, irrigation, etc.

What exactly is surface runoff harvesting?

Rainwater drains away as surface runoff in cities. This runoff could be captured and used to recharge aquifers using appropriate methods.

What exactly is a rooftop rainwater collection?

It is a method of collecting rainwater where it falls. Rooftop harvesting converts the roof into catchments, and rainwater is collected from the top of the house/building.

What are the parts of a rooftop rainwater harvesting system?

1. Drainages

2. Modes of transportation

3. Initial flush

4. Use a filter