The document covers rainwater harvesting as an essential technology for addressing global water supply challenges, particularly in light of population growth and the water crisis affecting billions. It explains rainwater harvesting systems, their components, applications, advantages, and disadvantages, highlighting their potential to supplement water supply for potable and non-potable uses. Key points include the necessity for effective systems and the consideration of both environmental and cost factors in their implementation.

1. WATER SUPPLY AND
TREATMENT TECHNOLOGY
(EHT 215)
LECTURER: SIR OAK

2. LECTURE SIX
 Rainwater harvesting
Learning objective:
After completing this topic, students should be able to:
• have a critical understanding of the need to promote rainwater
harvesting.
• explain the rainwater harvesting systems.
• state the merits and demerits of rainwater harvesting.

3. Introduction
• The issue of supplying adequate water to meet societal needs is one of
the most urgent and significant challenges faced by decision-makers.
• Rainwater harvesting is an excellent means of supplementing water for
both potable and non potable purposes.
• Rainwater harvesting describes processes in which precipitation that
falls on a site is diverted, captured, and stored for use on-site, as
opposed to allowing it to run off, evaporate, or infiltrate into the soil.

4. Why Should Rainwater Harvesting and Utilization be Promoted?
 Global Population Growth
• The United Nations indicate that global population is likely to
peak at about 8.9 billion in 2050.
• There have been profound demographic shifts due to rural
urban migration.
• Given that many water resources are already being polluted in
some regions; significant effort will be required to meet the
needs for water.

5. The Global Water Crisis
• 2.1 billion people globally do not have access to clean, safe
drinking water.
• 3.4 million people die each year from scarce and contaminated
water sources.
• At any given time, half of the world’s hospital beds are occupied
by patients suffering from diseases associated with lack of
access to clean water.
• Rapid population growth, combined with industrialisation,
urbanisation, agricultural intensification and water-intensive
lifestyles is resulting in a global water crisis.

6. Application of Rainwater Harvesting
Rainwater harvesting can be useful for installations with the
following issues:
Areas with water stress due to drought and arid environments.
On-site ground water wells that may require significant energy
to use such as deep wells and challenging treatment.
Areas with regulatory requirements to reduce peak flows,
lessening the erosive forces of storm water runoff.
Situations in which ponded surface water contributes to insect
or algae problems.

7. Uses of Rainwater
Rainwater can be harvested for a number of uses:
• Non-potable uses, such as toilet flushing, irrigation, dust control,
and vehicle washing.
NB: Some of these applications may require specialized
plumbing.
• Potable water uses including drinking water, food preparation,
showering, and washing.
NB: These applications would likely require treatment to
ensure that the water meets requirements for potable uses.

8. Rainwater Harvesting System
• The categorization of rainwater harvesting systems depends on
factors like:
the size and nature of the catchment areas and
whether the systems are in urban or rural settings.
• Some of the systems are as follows:
 Simple roof water collection systems
This comprises of the cistern, the piping that leads to the cistern
and the appurtenances within the cistern.

10. Rainwater Harvesting System cont…
 Larger systems for educational institutions, stadiums, airports,
and other facilities.
 Roof water collection systems for high-rise buildings in
urbanized areas.
 Land surface catchments
Ground catchment techniques provide more opportunity for
collecting water from a larger surface area. This technique is
mainly suitable for storing water for agricultural purposes.

11. Example of a ground catchment system.

12. Components of Rainwater Harvesting Systems
A rainwater harvesting system typically consists of three
basic components, namely:
(i) the catchment area,
(ii) the conveyance structures, and
(iii) Collection and storage equipment

14. The catchment area
• It is the area that gets rainwater directly.
• There are two main types of the catchment area, namely:
 Rooftop catchment - Here, rooftop of any building serves as
the catchment.
 The quantity and feature of this collected water are influenced by the
location, size, and material of the roof.
 Land surface catchment - Here, rainwater is collected from the
common surface of any ground or land.
 In this method, water is kept either in small storage reservoirs or in
small dams for irrigation purpose.

15. The conveyance structures
• These structures are the means to transfer the collected water
from catchment surface to the storing vessels.
• This structure consists of a number of downpipes attached to
the rooftop gutters.
• The pipes should be made of plastic, PVC or other inert
substance to avoid corrosion due to the low pH (acidic) of
rainwater.
• Water collected from the first rain may consist of dirt and debris.
Hence, it is required to do the primary treatment by clearing
those impurities.

16. The first part of each rainfall should be
diverted from the storage tank.
A good time to inspect gutters and down-
pipes is while it is raining.
Regular cleaning is necessary to avoid
contamination.

17. First flush diversion

18. Collection and storage equipment
• It can vary from simple types within a household to bigger
systems from which water is either gravitated or pumped to
water treatment plants.
• Storage tanks for collected rainwater may be located either
above or below the ground.
• Reinforced concrete, fiberglass, polyethylene, and stainless
steel are suitable materials.
• The tank needs to be fitted with tight cover for preventing algal
growth and the breeding of mosquitos.

19.  Galvanized iron tank

20.  Ferro-cement tank

21.  Plastic tanks

22. Collection and storage equipment cont…
The following devices are also desirable:
• An overflow pipe to drain excess water when the storage tank
is full.
• An indicator of the amount of water in the storage tank
• A vent for air circulation (often the overflow pipe can substitute)
• Protection against insects, rodents, vermin, etc. may also be
required.

23. Advantages of Rainwater Harvesting
• Rainwater is a relatively clean and free source of water
• Rainwater harvesting provides a source of water at the point
where it is needed
• It is owner-operated and managed
• It is socially acceptable and environmentally responsible
• It promotes self-sufficiency and conserves water resources
• Rainwater is friendly to landscape plants and gardens

24. Advantages of Rainwater Harvesting cont…
• It reduces storm water runoff and non-point source pollution
• It uses simple, flexible technologies that are easy to maintain
• Offers potential cost savings especially with rising water costs
• Provides safe water for human consumption after proper treatment
• Low running costs
• Construction, operation and maintenance are not labor-intensive.

25. Disadvantages of rainwater harvesting
• The main disadvantages of rainwater harvesting technologies
are the limited supply and uncertainty of rainfall.
• Low storage capacity will limit rainwater harvesting.
• High storage capacity will add to the construction and operating
costs making the technology less economically feasible.
• Storage tanks can be unsafe for small children if proper access
protection is not provided.

26. A simple and unique rainwater utilisation facility at the community level

27. Thank you