Memorandum submitted by John Meadley PhD
MBE
1. I would like to respond to one small
but important aspect of your enquiry into water and sanitation—and
that is concerning rainwater harvesting at the community level.
I am not a technical expert in the subject, although know some
who are[204]
but I have some practical experience over many years whilst working
in the developing world since 1968. My observations are simple
and I will leave it to the experts to develop the theme.
Dr Terry Thomas, Head of Development Technology Unit
and Sen Lect. School of Engineering, Warwick University
Ms Keziah Ngure, Chairperson, Kenya Rainwater Harvesting
Association
Dr Sayed Azim-Ali, Nottingham University
Professor Henry Mahoo, Sokoine University of Agriculture,
Tanzania
2. All the fresh water that is available
to us came from, or will come from, rainfall—and yet a significant
proportion of that rainfall is not captured and utilized but is
lost to the oceans, where it is diluted with salt water—often
causing considerable damage on its way through erosion. In the
popular mind the answer is to build large dams that will store
water, which may be used for supplying domestic and industrial
needs (after purification), for irrigation or for generating hydroelectric
power. Whilst such dams have obvious merits, they consume large
amounts of capital for construction and need extensive reticulation
systems that are both expensive to build and maintain and experience
significant levels of losses. In many cases, their construction
requires communities to leave their homes and be relocated—causing
much misery. However, few poor people in the developing world
benefit from such dams. The focus therefore needs to be on ways
of harvesting and storing water at the community level.
3. Rain falls almost everywhere—in
varying amounts and at different times of year. Hence virtually
everybody—whether rich or poor—can potentially
be involved in harvesting rainwater. In the UK, anyone with a
garden could have a water butt to collect water off the roof of
the house to water their garden in dry periods whilst every new
golf course could be required to construct a dam to supply its
irrigation needs. The needs and the opportunities are clearly
so much greater in the developing world.
4. Rainwater can be stored in the soil,
for use in growing crops, or it can be stored in containers such
as dams or tanks. It is generally much cheaper to store water
in the soil, which is its own store.
STORING WATER
IN THE
SOIL
5. Rain that falls onto forests or soil
that is covered with vegetation is trapped and slowly infiltrates
into the soil—some of which is retained in the soil for
future use whilst some slowly replenishes the groundwater and
emerges in springs and streams. Where there is little or no vegetation—as
a result of overgrazing, or where crops have been harvested and
not yet replanted—the water is not trapped in this way.
Once the surface of the soil is saturated, the surplus rain runs
off. Where the exposed soil is on a slope, this surplus rainwater
moves with increasing speed and volume, frequently taking the
topsoil with it. When the rainfall is intense the surplus rain
flows into low lying areas at increasing speed, often washing
away large amounts of soil—as well as roads and tracks.
When this happens, rainfall causes damage and loss rather than
feeding the next crop to be planted.
6. Much of the focus in both thinking and
action to date has been on preventing such damage by designing
and constructing soil conservation measures that channel the water
into grassed areas that do not erode, taking the water on into
the streams and rivers. However, whilst the damage is reduced,
the water runs away and is lost to the community. The logical
conclusion from this is to find ways of both preventing the damage
AND conserving the water through rainwater harvesting.
7. To harvest rainwater and retain
it with the soil, the rainwater must be slowed down, spread out
and allowed to infiltrate within the soil. This requires a range
of simple physical measures (to slow down the water—and
in some cases to channel it to where specific crops or trees are
growing) and to open up the soil surface so that the rainwater
can infiltrate more easily. The capacity of the soil to retain
that rainwater can also be increased by improving the structure
of the soil—through the addition of organic matter. The
advantage of retaining the rainwater within the soil is that it
is not necessary to construct new storage capacity—the soil
itself serves as the reservoir and any surplus is fed into the
ground water system.
STORING RAINWATER
FOR DOMESTIC
OR FARM
USE
8. To harvest rainwater for domestic use
or for watering livestock on a small scale it is necessary to
channel the rainwater into a place where it can be stored. Typically
this is a dam, from which water can be taken to where it is needed
by gravity feed or by using a pump. Since this is already a mainstream
activity that will not be considered further here.
9. Water can also be collected from the
roofs of dwellings for domestic use. Whilst collection is easier
from a tiled or tin roof, rainwater can also be collected (although
less efficiently) even from thatched roofs. This requires both
guttering to channel the water as it falls and a tank to store
the water. A roof with an area of 20 sq metres in an area of 500
mm of rain could theoretically produce 10 cu.m of water—or
10,000 litres, providing a family of five people with around 5
litres of water per person per day. In practice, there would be
some wastage (during periods of heavy rain); but at even 2.5 litres
per day of clean water this is significantly more than is available
to millions of people. There is a range of options for storing
water—from underground hafirs, to tanks made of plastic
or metal or cement. Perhaps the most famous is the Thai jar, of
which there are around 1.5 million in Thailand. The indicative
of cost of a tank (made of plastic/metal/concrete) with a capacity
of 10,000 litres (sufficient to hold water for the length of the
dry season) would be in the region of £400—at an average
capital cost of £40/m3 stored.[205]
Thus it is the cost of providing the storage tank that is the
major constraint.
10. Rainwater harvesting is not an area
of mainstream research. Over the years there have been, and continue
to be, a number of enthusiasts undertaking research and finding
practical ways of harvesting water. However, they have been viewed
in much the same way as organic farmers were until very recently.
There is now an opportunity to bring rainwater harvesting into
the mainstream.
11. In conclusion, this note seeks to increase
the awareness of the committee on the potential for rainwater
harvesting. Unlike large dams, that require high levels of capital
investment in storage and reticulation, everyone can harvest rainwater—either
to increase the amount of water in the soil to increase its productivity
or to meet some of their domestic needs for drinking, cooking
or washing. Rainwater harvesting is a neglected subject, but one
which has significant potential to increase the access of poor
people to water. The committee is asked to include in its recommendations
a greater focus on research into the options for, and the physical
implementation of, measures for ordinary people in the developing
world to harvest and store rainwater.
October 2006
204 Raymond Auerbach of the Rainman Landcare Foundation Back
205
This is based on communications over the past three months with
the Kenya Rainwater Harvesting Association (KRHA). I have been
dealing with them as part of the link that we have established
between Kings Stanley Junior School in UK and Kavuka Primary School
in rural Kenya (near Mariakani, Coast Province). This link came
about as a result of my working in rural Kenya and being a governor
of Kings Stanley Junior School. Funds raised by our pupils are
being used to build rainwater storage capacity at Kavuka, to designs
agreed with the KRHA. Back
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