Rainwater Harvesting in Buildings
Rainwater harvesting is a water conservation method that involves understanding the value of rain and making optimum use of rainwater at the place where it falls. Without rainwater harvesting, we depend entirely on secondary water sources like rivers and lakes, unaware that rain is the primary and ultimate source of water that feeds the secondary sources.
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| Fig.1. Rainwater Harvesting in Buildings |
Rainwater harvesting must not be considered as a technology that is opted for areas where water is limited. But it must be considered as one of the remedial and sustainable option for the water crisis that humans are going to face in the future. The technology helps conserve potable water, reduce urban runoff and mitigate flood risks.
As most of the land area is taken over by buildings, it is paramount to discuss how rainwater can be conserved and reused from buildings and areas surrounding it.
Most of the rainwater harvesting systems fail due to the lack of knowledge on rain, hydrological cycle and related parameters that are necessary to be studied for the performance of an effective rainwater harvesting system.
This article is an overview of the concept of rainwater harvesting and its implementation with building systems. Let's dive in!
What is Rainwater Harvesting in Buildings?
Rainwater harvesting can be defined as the process of harvesting rainwater falling on earth, before it joins the water courses, from where its collection is either limited or costly. (Fig.1)
Rainwater Harvesting in Buildings can be defined as the process of collecting the rainwater that falls on a building or its premises and using it for various purposes.
Uses of Rainwater Harvesting Technology
The rainwater harvesting technology can be used for two major sectors:
- General-purpose Use
- Recharging the groundwater
1. General Purpose Use
From drinking to cutting metals, the buildings of different occupancies require water. Irrespective of the purpose, rainwater water harvested can be properly treated and used for all general water demands of the building. A normal technique used for the installation of a general-use rainwater harvesting system in a building is :
- Collecting rainwater from suitable catchments
- Flushing out the first rainwater
- Storing the rainwater
- Qualifying rainwater according to the purpose of use
- Supplying rainwater to the points of use
- Draining excess rainwater
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| Fig.2. General Purpose Use Rainwater Harvesting System |
2. Recharging Groundwater
Over-extraction of groundwater due to increasing water demands of the occupants in the buildings results in various hydro-geological problems. This leads to the lowering of groundwater levels and its depletion. Hence, it is necessary to recharge groundwater. (Fig.1)
One of the effective methods to do this is by recharging groundwater using rainwater. Various functional techniques used for this include:
- Collecting rainwater from suitable catchment
- Conveying rainwater to the recharge structure
- Qualifying rainwater according to the method of recharge adopted
- Draining excess rainwater.
Key Components of a Rainwater Harvesting System
The major components of a rainwater harvesting system (Fig.3) are:
- Catchment area
- Conveyance System
- Rainwater Pre-filter System
- Storage Tank System
- Filtration System
- Distribution System
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| Fig.3. Components of Rainwater Harvesting System in Buildings |
1. Catchment Area
The roof or other surface that collects rainwater.
Typically, rooftops are the most common catchment areas. The size and material of the catchment area influence the quantity and quality of rainwater collected.
2. Conveyance System
Includes gutters and downspouts to channel rainwater from the roof to the storage tank.
Proper design and maintenance of the conveyance system are essential to prevent water loss and contamination.
3. Pre-Filters
Filters are installed to remove debris, leaves, and other contaminants from rainwater before it enters the storage tank.
Helps maintain water quality and prolongs the life of the storage tank and filtration systems.
4. Storage Tank
Stores collected rainwater for later use.
Can be made of various materials like polyethylene, concrete, or fiberglass.
The size of the tank depends on the catchment area, rainfall patterns, and water demand.
5. Filtration System
Filters the stored rainwater to remove impurities and make it suitable for various uses.
Common filtration methods include sediment filtration, carbon filtration, and UV disinfection.
6. Distribution System
Delivers filtered water to various points of use, such as taps, toilets, and irrigation systems.
Can be a simple gravity-fed system or a more complex system with pumps and pressure tanks.
What to Consider When Selecting Rainwater Harvesting System Components?
To ensure the success of your rainwater harvesting system, consider the following questions:
1. Budget
- What is your budget for the rainwater harvesting system?
- How much are you willing to invest in initial costs and ongoing maintenance?
- What is the quality of your roof catchment area?
- How much water can you potentially collect based on your roof size and local rainfall patterns?
- What are the specific water quality standards for your intended uses?
- What is your estimated daily water usage for non-potable purposes like irrigation and toilet flushing?
- How much storage capacity is needed to meet your water demand, especially during dry periods?
- Will the harvested water be used for potable purposes (drinking, cooking) or non-potable purposes (irrigation, flushing)?
- What level of treatment is required to meet the desired water quality?
- Are there any local building codes, permits, or water quality standards that need to be followed?
- How do these regulations impact the design and installation of your rainwater harvesting system?
Read More: Sources of Water - Water Supply Engineering
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