As quoted by David Suzuki, “Water is our most precious resource, but we waste it, just as we waste other resources, including oil and gas.” The rapidly increasing population, urbanisation and industrialisation have increased the demand for water supply manifold. In such a situation, rainwater harvesting is a fast-emerging and sustainable solution to help solve the water crisis in both rural and urban segments. It is an ancient practice.
Gharpedia brings you the multiple benefits of rainwater harvesting; rainwater harvesting models and their basic components; the suggested amounts of rainfall that can be collected; various ways of collecting rainwater along with their pros and cons; and uses of the collected water.
What is Rainwater Harvesting?
Rainwater harvesting is a sustainable practice that involves the collection and storage of rainwater from the surfaces where it falls, intending to use this stored water at a later stage for domestic, commercial, or agricultural purposes. According to CPWD, “rainwater harvesting is a technique recognised to conserve naturally available pure water through rainfall.” It is free from any kind of impurity, with relatively less storage cost and no maintenance cost involved except for periodic cleaning. Reserving rainwater can help recharge local aquifers, reduce urban flooding and most notably, ensure water availability in water-scarce zones.
Benefits of Rainwater Harvesting
Here’s a list of a few benefits of rainwater harvesting, which is a socially acceptable and environmentally responsible initiative for households:
- Promotes water conservation by reducing dependence on groundwater and municipal water.
- Saves money on water bills
- Provides one with an excellent and valuable source of water in emergencies.
- Easy to install, operate, and maintain for all types of houses and in all areas (rural, sub-urban and urban) with minimal investment.
- Reduces rainwater runoff and solves drainage problems.
- Provides an ideal solution in areas facing dire water shortages.
- Sizeably reduces the consumption of potable water – Decrease load on the storm water disposal system.
- Provides a relatively clean and free source of water.
- Facilitates total control over one’s water supply.
- Promotes self-sufficiency.
- Offers a competitive water solution for landscape plants and gardens as it is non-chlorinated.
- Can be easily retrofitted to an existing structure or installed during the construction of the house.
- Provides extremely flexible and modular systems, thereby facilitating expansion, reconfiguration, or relocation, if need be.
- It cuts down on the energy cost of water movement as the collection source and usage points of harvested water are proximal.
- Improves groundwater quality and decreases salinity (by dilution)
- No land is wasted for storage purposes, and no population displacement is involved.
- Storing water underground is environment-friendly.
- Mitigates the effect of drought
- The subsurface aquifer also serves as a storage and distribution system.
Rainwater Harvesting Models
There are broadly two models associated with rainwater harvesting at the domestic level:
Rural Model of Rainwater Harvesting
In the hinterland, where the roofs of houses are generally built with sheets or Mangalore tiles, rainwater easily flows to the edges, facilitating its collection through gutters. Denizens then filter the rainwater through a fine cloth. This collected water is used for domestic purposes, agricultural needs, or fulfilling the needs of livestock.
Urban Model of Rainwater Harvesting
In urban locales, rainwater from the roof of the house is collected through rainwater gutters and stored in a storage tank, thereby supporting both the potable (post-water treatment) and non-potable needs of the family at their doorstep.
Basic Components of Rainwater Harvesting for House Systems
- A catchment area, which is generally the rooftop of the house.
- A conveyance system (perhaps piping) to help the captured rainwater travel from the roof to the storage area.
- A storage system (say, a barrel, cistern, or tank) to contain the rainwater for future use.
- A distribution system to transfer the water from storage to the usage area.
How Much Rain Can Be Collected?
The following formula can help you decide the amount of rainfall that you can collect from the terrace area:
1″ of rain x 1 sq. ft. = 0.623 gallons i.e. 2.8 liters or 1 cm of rain x 1 sq. ft. = 0.01m3
i.e. 10 liters.
For 1000 sq.ft. (terrace area), 2.8 x 1000 = 2800 litres of water (within 1” of rain).
If annual rainfall is 30”, 2800 x 30 = 84000 litres of water (provided there is much storage capacity).
Normal tankers have a 5000 litre capacity, so you can harvest almost 16 to 17 tankers of water. Please note that our total daily water demand is 70 to 135 litre/day per person, depending on one’s lifestyle. Thus, a family of five can store the water required for about 125 days.
If you are confused about which type of tank can be used for collecting rainwater, then this article will help you choose the right one as per your needs.
Plastic vs Concrete Water Tanks: Make a Right Choice
Methods of Rainwater Harvesting
There are two types of rainwater harvesting techniques: surface rainwater harvesting and rooftop rainwater harvesting.
01. Surface Runoff Harvesting
Surface runoff water harvesting is a method of rainwater harvesting in which stormwater is accumulated, and purified for use. Rainwater flows away as surface runoff in developed areas. This runoff can be caught and used for recharging aquifers by adopting proper methods.
How much water can be harvested?
According to CPWD, “The total amount of water that is received in the form of rainfall over an area is called the rainwater endowment of that area. Out of this, the amount that can be effectively harvested is called rainwater harvesting potential.
Rainwater harvesting potential = Rainfall(mm) × collection efficiency
Annual rainfall of any city/place (say) 600mm
Area of roof catchment 100sqm
Volume of rainfall over the plot = Area of plot × height of rainfall
Rainwater endowment of that area = 100 sqm × 0.6 m = 60 cum
= 60,000 liters”
02. Rooftop Rainwater Harvesting
It is a system of storing rainwater where it falls. In rooftop harvesting, the roof becomes the catchment, and the rainwater is collected from the roof of the house or building. It can either be stored in a tank or diverted to an artificial recharge system. This method is less expensive and very effective, and if implemented properly, it helps augment the groundwater level of the area.
Rooftop rainwater harvesting and conservation systems, both small and large, are comprised of six basic components, as described below:
- Catchment Area/Roof: The surface upon which rain falls
- Gutters and Downspouts: Transport channel from catchment surface to storage
- Leaf screens and Roof washers: These are systems that remove contamination and debris.
- Cisterns or storage tanks: where collected rainwater is stored
- Conveying: The delivery system for treated rainwater, either by gravity or pump
- Water treatment: filters, equipment, and additives to settle, filter, and disinfect.
This system involves collecting water that falls on the zinc, asbestos, or tile roof of a house drain or collector and sending it to a nearby covered storage unit or cistern. Rainwater yield varies with the size and texture of the catchment area. A smoother, cleaner, and more impervious roof contributes to better water quality and quantity.
Different Ways of Collecting Rainwater
All the methods mentioned below imbibe the same principles but differ in the scale of the system, the aesthetics, and the effectiveness of water conservation.
01. Rain Barrels Method of Rainwater Harvesting
All the methods mentioned below imbibe the same principles but differ in the scale of the system, the aesthetics, and the effectiveness of water conservation.
One of the simplest, most popular, and most people-friendly methods is to install a barrel at a gutter downspout to collect the rainwater. Based on the carbon footprint one wishes to save, this barrel could be either recycled or commercial.
Pluses
- Easy to adopt.
- Barrels are easily available at offline stores or on e-retail platforms.
- Barrels occupy a limited area, so they are the best solution for small spaces.
Minuses
- Limited storage capacity: around 50 to 100 gallons i.e. 225 to 450 litres.
- If unmonitored, it escalates the risk of water going to waste as the barrel may overflow, thereby defeating the very purpose of rainwater harvesting!
Dry System of Rainwater Harvesting
A slight variation of the rain barrel set-up entails a larger storage volume. To put it in a nutshell, the collection pipe “dries” after each spell of rain since it empties directly into the top of the tank.
Pluses
- Capacity to store a large amount of rainwater.
- Extremely apt for climates where rainfall occurs with infrequent, larger storm events.
- It is quite economical to install.
- Ease of maintenance owing to a simple system.
Minuses
- The storage tank must be next to your house.
If you are using a plastic water tank as a storage tank, then you must read this blog on plastic water tanks for your safety.
Wet System of Rainwater Harvesting
This system entails the placement of collection pipes underground to connect multiple downspouts from different gutters. The mechanism is quite innovative: as the rainwater fills the underground piping, the water levels in the vertical pipes rise, leading to the spilling of the water into the tank. Certain mandates for the wet system comprise: water tight connections for the downspouts and the underground collection piping; and ensuring that the elevation of the tank inlet is below the lowest gutter on the house.
Pluses
- Capacity to gather and conserve rains from the entire collection surface.
- Ability to collect from multiple gutters and downspouts.
- Tanks can be set up away from your house.
Minuses
- Steeper costs due to underground piping.
- Mandate for the availability of a sufficient difference between the gutters and tank inlet.
We have also written an article about the benefits of gutter cleaning. Have a look into it.
3 Benefits of Gutter Cleaning that You Never Knew Existed!
Precautions for Rainwater Harvesting
- If one intends to use rainwater as a potable source, then a filter mechanism is a must.
- Allow the water collected from the first rain of the season to drain, as it might contain pollutants from the terrace, roof, etc. For this, one needs to have a small valve installed at the bottom of the tank pipe, so that the water from the first rain drains out.
- Those living in highly polluted areas (due to the emission of gases and suspended particles by industries) must refrain from rainwater harvesting.
Uses of Collected Rainwater
From a broader perspective, we can deploy rainwater anywhere we use tap water. Expending drinking water to flush our toilets and water our lawns reeks of wastefulness and irresponsibility, keeping in view the growing population vis-à-vis the gross shortage of water across the country and even the world. The collection of rainwater not only lends a green hue to our homes but also reduces our environmental footprint.
Rainwater can be tapped for irrigation, non-potable and potable uses.
Some specific uses of rainwater include,
- Watering the lawn and plants in our garden by connecting the rainwater collection system to the irrigation/sprinkler system
- Washing our vehicles and pets
- Refilling our fountains, fish ponds, and swimming pool
- Washing our driveways and sidewalks.
- For all indoor non-potable fixtures, say, for example, toilets, washing machines, dishwashers, etc.
- Post-adopting adequate filtering and disinfection methods, use it for all potable needs.
- For industrial processes in place of municipally treated water
So, what are you waiting for? This Environment Day resolve to do your bit for Mother Nature by taking a small but meaningful step towards selecting the most convenient rainwater harvesting practice from the ones Gharpedia has shared with you…
For those green warriors who wish to reduce the demand on mains water supply, hope exists in the form of roof top and surface runoff rainwater harvesting methods. Opting for a compatible rainwater harvesting system is critical for making your home more sustainable.
Rainwater is one of the purest sources of water available at everyone’s doorstep at zero cost.
Rainwater is a free and universally available commodity. Harvesting rainwater also becomes free after recouping the capital cost of the infrastructure collection system.
Image Courtesy : Image 1, Image 2, Image 3, Image 4, Image 5, Image 6, Image 7, Image 10
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Author Bio
Huta Raval – An English Literature and Journalism Topper, Huta Raval has graduated from the L D Arts College, Ahmedabad. Post serving for 23 years in the NBFC and Public Library Sectors her desire for ‘writing the unwritten’ brought her to the creative field of content writing. Her clientele comprises of NGOs, Blogging Platforms, Newspapers, Academic Institutions, et al.