rainwater harvesting

Category: Education

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How to harvest rainwater. Things one can do to get access to clean water


Presentation Transcript

Rainwater Harvesting Solution to water crisis:

BioV 436 Hussein J. Kanbar Rainwater Harvesting Solution to water crisis 1


Introduction Rainwater harvesting (RWH) is a wide range of technologies used to collect , convey and store rain - before it reaches the aquifer- for later use from relatively clean surfaces such as a roofs , land surfaces or rock catchment areas . 2 Stormwater harvesting is a subdiscipline of rainwater harvesting. In this case, water is collected from the ground .


RWH 3 Today, rainwater harvesting has gained much significance as a modern , water-saving and simple technology. It has been practiced for over 4,000 years throughout the world, traditionally in arid and semi-arid areas. Rainwater is usually clean water that has undergone natural distillation , but it may be associated with some human-made airborne particles or pollution.

Who can own a RWH system?:

Who can own a RWH system? 4 An individual house of an average area of 300-500 m 2 . An apartment building , the cost will be less since many people will share the cost. A colony , the cost will be much less. An institution such as a hospital or school.

Water usage:

Water usage Use Liters consumed by a person per day Drinking 3 Cooking 4 Bathing 20 Flushing 40 Washing clothes 25 Washing utensils 20 Gardening 23 Total 135 Many countries face difficulties providing that volume to their citizen. Another source of low cost water is needed. Rainwater harvesting is able to provide a solution 5

Objectives of RWH:

Objectives of RWH Increase ground water availability during periods of requirement. Decreasing menace of floods , especially in urban areas. Enhance the quality of the environment. Provide a source of water in places where: There is no surface water Water is inaccessible Water is too salty or inappropriate to use 6

Classification of Rainwater Harvesting:

Classification of Rainwater Harvesting The practice of collecting rainwater from rainfall events can be classified into two broad categories : land-based and roof-based . Land-based rainwater harvesting occurs when runoff from land surfaces is collected in dikes, ponds, tanks and reservoirs . Roof-based rainwater harvesting refers to collecting rainwater runoff from roof surfaces which usually provides a much cleaner source of water. 7

Other classification of RWH:

Other classification of RWH Rainwater harvesting can also be classified according to the type of catchment surface 8

Why rainwater harvesting? :

Why rainwater harvesting? The earth is known as the Blue Planet for a reason. The world’s current challenge is to improve the planet's water quality and then maintain it clean and healthy. Clean drinking water is not always available. Rainwater is a free source and relatively clean, and with proper treatments, it can be even used as a potable water source . Rainwater harvesting relieves the pressure on the environment by mitigating floods, soil erosions and replenishing groundwater levels . 9

Application areas :

Application areas Rainwater harvesting systems can be installed in both new and existing buildings. Harvested rainwater can be used for different applications that do not require drinking water quality such as toilet flushing, garden watering, irrigation, cleaning and laundry washing . As rainwater is very soft, there is also less consumption of washing and cleaning powder . 10

Components of a rooftop rainwater harvesting system :

Components of a rooftop rainwater harvesting system Although rainwater can be harvested from many surfaces, rooftop harvesting systems are most commonly used, as the quality of harvested rainwater is usually clean following proper installation , maintenance and treatment . Rainwater harvesting systems generally consist of six basic elements: 11 Storage facility, cisterns or tanks Purification Delivery system Collection (catchment) area Conveyance system Filtration

Design Considerations:

Design Considerations 12 Three most important components should be considered: Hydrogeology of the area including nature and extent of aquifer, soil cover, depth to water levels and chemical quality of ground water. Area contributing for runoff, i.e. how much area and land surface pattern are suitable for the flow of water. Hydro-meteorological characters like rainfall duration, general pattern and intensity of rainfall.

RWH system:

RWH system A simple schematic diagram of a rooftop rainwater harvesting system. 13

1. Collection Area:

1. Collection Area A collection or catchment system is generally a simple structure such as roofs that direct rainwater into the conveyance system . Roofs are ideal as catchment areas as they easily collect large volumes of rainwater. 14

1. Collection Area:

1. Collection Area The amount and quality of rainwater collected from a catchment area depends upon the rain intensity, roof surface area, type of roofing material and the surrounding environment . 15 Roofs should be constructed by chemically inert materials . If paint is used, it should be non-toxic (no lead-based paints).

2. Conveyance system:

2. Conveyance system A conveyance system consists of pipes and gutters. It transfers the rainwater from the roof catchment area to the storage system via pipes from the roof top to one or more downspouts. 16

3. Filtration:

3. Filtration Before water is stored in a storage tank or cistern, and prior to use, it should be filtered to remove particles and debris . 17

First flush and filter screens :

First flush and filter screens The roof is full of dust, bird droppings, leaves, etc . To prevent these pollutants from entering the storage tank, the first rainwater containing the debris should be diverted or flushed . It is recommended to use automatic devices that prevent the first 20-25 liters of runoff from being collected in the storage tank. Screens to retain larger debris such as leaves can be installed. Simple gravel-sand filters can also be installed. 18

4. Storage facility:

4. Storage facility Storage tank or cistern is used to store harvested rainwater . The storage tank should be also constructed of an inert material . Polyethylene tanks are the most common and easiest to clean and connect to the piping system. Storage tanks should be also kept closed. Storage tanks must be opaque to inhibit algal growth. 19

4. Storage facility:

4. Storage facility Depending on the space available, the storage facility can be placed above ground surface or under , or directed to recharge groundwater. 20

Storage tanks or reservoirs :

Storage tanks or reservoirs The storage reservoir is usually the most expensive part of the rainwater harvesting system. The reservoir must be constructed in such a way that it is durable, watertight, holds water pressure and the collected water does not become contaminated . All rainwater tank designs should include as a minimum requirement: 21 An overflow pipe: a manhole and drain to facilitate cleaning. A solid secure cover A coarse inlet filter

5. Purification:

5. Purification The harvested rainwater can be suitable for drinking as well as domestic uses. Disinfection of the harvested rainwater includes ozone or UV disinfection, this is necessary if rainwater is to be used as a potable water source. 22

6. Delivery system:

6. Delivery system Delivery system delivers rainwater and it usually includes a small tap or pump, and a pressure tank. For easier access, it is better to install the tank in a way that the collected rainwater can be retrieved by gravity. Collection area Conveyance Conveyance Filtration Tank Purification Pump 23

Simple methods:

Simple methods 24 A simple system usually consists of a catchment area and a means of distribution , which operates by gravity . The water is deposited in a landscape holding area , a concave area or planted area with “edges” to retain water, where it can be used immediately by the plants .

Simple methods:

Simple methods 25 Crescent-shaped landscape holding areas on a slope. Parking lot curb cut-out directing water into planted areas.

Simple methods:

Simple methods 26 Rain harvesting is possible on an individual scale and can come up with great advantages. This method can be easily constructed, even in front of your house. The tank can even be hidden by simple methods.

RWH in the driveway:

RWH in the driveway 27 Roof catchment with sloping driveway and underground storage. The stored water can either be pumped or flown by the act of gravity to nearby planted areas. It is preferred to use a filter.

Lebanon rainfall:

Lebanon rainfall Average annual rainfall in Lebanon is 860 mm . Four months during the year show approximately no rainfall. Some aquifers get dry during this period. 28

Water deficiency:

Water deficiency With an estimated minimum water consumption of 20 L/person/day , the annual water demand will be = 20 x n x 365 L/year , where n=number of people in the household. If n=5, then the annual water demand is 36,500 liters. In Lebanon, in a four months dry period, the required minimum storage capacity would be about 12,000 liters . 29

Water deficiency:

Water deficiency As rainwater supply depends on the annual rainfall, roof surface and the runoff coefficient, the amount of rainwater that can be collected can be calculated by the following formula: S = R x A x Cr As an example: a metal sheet roof of 80 m 2 with 860 mm rainfall/year will yield = 80 x 860 x 0.8 = 55,040 L/year. 30 S = Mean rainwater supply in L R = Mean annual rainfall in mm/year A = Surface area of catchment in m 2 Cr = Run-off coefficient

Types of rainwater use :

Types of rainwater use Rainwater systems can be classified according to their reliability , yielding four types of user regimes: Occasional: water is stored for only a few days in a small container . This is suitable when there is a uniform rainfall pattern with very few days without rain and when a reliable alternative water source is available. Intermittent: in situations with one long rainy season when all water demands are met by rainwater. During the dry season, water is collected from other sources. 31

Types of rainwater use :

Types of rainwater use Partial : rainwater is used throughout the year but the 'harvest' is not sufficient for all domestic demands. For example, rainwater is used for drinking and cooking, while for other domestic uses (e.g. bathing and laundry) water from other sources is used. Full: for the whole year, all water for all domestic purposes comes from rainwater . In such cases, there is usually no alternative water source other than rainwater, and the available water should be well managed, with enough storage to bridge the dry period. 32

Cultural acceptability :

Cultural acceptability Rainwater harvesting is an accepted freshwater augmentation technology in many parts of the world. While the bacteriological quality of rainwater collected from ground catchments is poor , rainwater from properly maintained rooftop catchment systems , which are equipped with tight storage tanks and taps, is generally suitable for drinking and often meets the WHO drinking water standards. 33

Benefits of rainwater harvesting :

Benefits of rainwater harvesting Rainwater harvesting in urban and rural areas offers several benefits including provision of supplemental water, increasing soil moisture levels for urban greenery, increasing the groundwater table via artificial recharge, mitigating urban flooding and improving the quality of groundwater. 34


Advantages 35 Relatively clean and free source of water Provides a source of water when needed Owner-operated and managed Socially acceptable and environmentally responsible Promotes self-sufficiency and conserves water resources Reduces stormwater runoff and non-point source pollution Offers potential cost savings Provides safe water for human consumption


Disadvantages Supplies can be contaminated by bird/animal droppings on catchment surfaces and guttering structures unless they are cleaned/flushed before use. Poorly constructed water cisterns or containers can suffer from algal growth and invasion by insects, lizards and rodents. They can act as a breeding ground for disease vectors if they are not properly maintained. Limited supply and uncertainty of rainfall. Rainwater is not a reliable water source in times of dry periods or prolonged drought. Low storage capacity which will limit rainwater harvesting. 36


Finally 37 Only 2.5% of the earth’s water is fresh. A big part run-offs to oceans and seas. Why to lose all that water?? Play your part and harvesting rainwater After all None of this will work unless… The citizens make rainwater harvesting their own business

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