Newsletter and Technical Publications
<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Some Countries in Asia>
3.7 Rainwater Harvesting for Multiple Purpose Use
This technology employs one of the oldest methods of rainwater
harvesting in Bangladesh; namely, the use of the roof of a house to collect
rainwater, and, by means of a gutter, convey the collected water to a pot for
immediate use or to a storage place for later use. This system of rainwater
harvesting is associated with various kinds of roofing materials including
cement, corrugated iron (C.I. sheeting), thatched straw, etc. These roofing
materials span the gamut of materials found within a community: cement roofed
houses tend to be owned by the richer persons in a community, corrugated iron
sheet roofed houses by the middle income persons, and the thatched roof houses
by the poorer segments of the community. Gutters, too, are made from different
materials, including corrugated iron sheets, palm wood, betel nut wood, bamboo,
and banana plant leaves, etc. Storage pots are also of different types, ranging
from earthen jars, locally called motkas which are of three different sizes,
small, medium and large; to oil drums; to cemented tanks with steel fabricated
covers. For immediate use, water is usually collected in buckets or wide-mouthed
pots locally called gamlas. Sometimes, medium or large underground or above
ground cement water tanks are also constructed where large quantity of water is
to be stored. Rainwater from the gutters may also be stored in ditches around
the house. Large earthen jars or cement storage tanks with steel plate covers
are generally used by the wealthier section of the community and are
semi-permanently placed inside or immediately outside of the house. In all
cases, the harvested rainwater is used to meet household demand for such needs
as bathing animals, washing dirty clothes, and other nonpotable purposes.
Figure 14. Rainwater Harvesting from a Corrugated Iron Roof
In the case of cement roofed houses, water storage tanks are generally
constructed immediately below the roof with an opening at one side. Rainwater is
directed to the storage tank by erecting a 3" to 4" brick-cement
boundary. The slope is adjusted in such a way so that rainwater automatically
runs into the storage tank through the opening. The opening can be closed with a
steel plate cover. The boundary also has an opening which is used to bypass the
storage tank and convey excess rainwater through a PVC pipe to the ground. The
water from the storage tank is provided to the lower floors of the house through
rubber piping, and abstracted through a plastic tap.
In the case of corrugated iron roofed houses, the corrugated iron sheets are
usually inclined at angles between 30 and 40 degrees. Water collected in gutters
placed at the lower edge of the corrugated iron sheeting is conveyed by gravity
into motkas as shown in Figure 14. Water is supplied to the user through opening
in the top of the motka which is usually kept covered.
Figure 15. Palm Wood Guttering Used to Capture Water
Figure 16. Storage Tanks
In the case of straw roofed houses, the thatch is also generally inclined at
an angle of between 30 and 40 degrees. Water running off the thatch is collected
in palm wood or bamboo gutters and conveyed into motkas or buckets at the
convenience of the household as shown in Figures 14 and 15. In each case, the
first flush of rainwater is allowed to flow out as the storage container as it
is generally very dirty. The subsequent water is stored in the motkas or other
Extent of Use
In places where there are chronic freshwater shortages, like Gourikhali,
Kumkhali, Dacope, Ramnagar, Kaulashganj, and Shyamnagarin in the southwest of
Bangladesh, rainwater obtained using roof catchments is used throughout the year
for household purposes (see also the previous discussion of rainwater harvesting
for domestic water supply use). Elsewhere in the southwest of Bangladesh,
rainwater is used to supplement available water through January and February. In
other parts of the country, rainwater is usually used for meeting immediate
household needs such as bathing, feeding cows, washing clothes and dishes, etc.
The stored water retains its colour and taste for about two months after the
Figure 17. Storage Jars for Household and Barnyard Use.
A significant number of people living in saline areas without access to
tubewells at reasonable depths or other suitable surface water sources use
rainwater for drinking purposes as well as other household purposes like
cooking, washing and bathing. When people do not use rainwater, it appears to be
the lack of suitable storage pots or lack of knowledge of the technology for
harvesting rainwater. Such persons often make use of other water sources such as
ponds, which are usually contaminated. Rooftop rainwater harvesting has also
been observed in hilly areas of Mymensingh District, where most middle class
families were observed to use rainwater for washing and other nonpotable
Operation and Maintenance
Maintenance of rainwater harvesting systems is simple, consisting of the
cleaning of catchment areas, conveyance systems, and storage devices.
Level of Involvement
This technology is implemented at the household level.
Effectiveness of the Technology
Unless carefully constructed and managed, the quality of the water stored in
the motkas gradually deteriorates as a result of infestation by insects and
pests, settling of dust, breeding of mosquito larvae, etc. However, if the
stored rainwater is filtered and the lid of the storage container tightly closed
after each use, its quality can be maintained up to two months. If storage is
prolonged, the stored water may acquire odours and its colour may change.
Previously, local Koi, Singh or Magur fish ( Anabas testudinews,
Heteropreutes sp., Clarias batrachus) were used to eat the mosquito larvae
and other insects. However, these fishes also discharge their own excreta into
the water which degrades the quality of water. As people have become more
conscious of these facts, the use of fish for maintaining water quality is fast
decreasing. If these fishes are grown at all, they are harvested for
consumption. Currently, people sometimes use alum or other locally made
flocculent aids like burnt shell to clarify the water. Water purifying tablets
are very infrequently used.
Generally, the availability of a means to purify the stored water is a severe
constraint to maintaining rainwater quality; usually well-to-do families
practice sound preservation procedure, while to disadvantaged cannot afford to
do so as they do not have motkas of an appropriate size and may lack the cash
necessary to buy flocculent aids. In extreme cases, the poor use contaminated
rainwater stored in inappropriate containers or use dirty pond water.
This technology is suitable for use in areas with adequate rainfall.
The capital cost of this technology is associated mainly with the purchase
and installation of the gutters and storage tanks. The cost of the gutters
varies depending on the type, ranging from $1.00 to $1.50 for bamboo, $4.00 to
$5.00 for palm wood, and $10.00 to $15.00 for corrugated iron sheet.
Rainwater harvesting is a relatively inexpensive and popular technology.
Disadvantages of harvesting rainwater include contamination by pollutants
from the roof mixing with the water, and degradation of the stored water due to
contamination by toads, mosquitos, cockroaches, etc.
There are no known problems associated with the use of this technology.
Further Development of the Technology
HEED-Bangladesh, an NGO located in Dacope, stores water in a fibre glass tank
pumped by centrifugal pump from a nearby rainwater pond. Water tanks could also
used in conjunction with such a pumping system to store rainwater on the
Mohammed Aslam, Saleh Ahmed Chowdhury, Alamgeer Faridul Hoque,
and S.R. Sanwar, Intermediate Technology Group, House 32, Road
13A, Dhanmondi, Dhaka, Bangladesh, Tel. 880 2 811 934, Fax: 880 2 813 134,