2. Rain water harvesting for Nong het district, Xiangkhouang Province
12 target villages
Synopsys
Study into alleviation of dry season water shortage in 12 target villages in Nong het district by use of
rain water harvesting systems.
Scope
The scope of study is an initial look at the possibility and methodology of harvesting rain water in the
12 target villages to supplement their existing spring water & domestic rain water harvesting supply,
particularly for the ‘lean’ months in the dry season. The study was conducted over two days with
presentation of initial results at the CF Nong Het office.
General Notes
This report covers both generic and specific solutions for the proposal for rainwater harvesting
systems. The general notes also covers other issues which could be considered outside the scope of
this report. However not all problems and solutions can be considered in isolation, therefore they
have been included. The report concludes with notes on specific villages visited.
Loss of water from existing system
It has been recognised by CF and also observed during the study that the loss of water through:
1. Brocken pipes (often due to construction work)
2. Lost, stolen or broken taps
3. Taps being left on
4. Illicit ‘tapping’ of water pipes
Before any supplementary water system can be examined, attention must be made to these existing
water loss problems.
In the issue of taps, the taps supplied are inferior Chinese manufacture and are easily broken or
stolen or just left on.
The resolution of this issue can be approached in two different ways:
1. Education program on the need for conserving water.
A very easy statement to make but as CF will know a very very difficult concept to
implement. This would be a program that would take several years to implement but a long
persistent program will achieve results in the end.
3. 2. Installation of ‘tamper proof’ tap timer switches in the village cisterns.
As this issue is not covered in the report no resources have been used in sourcing such a tap
(if one exists)
The layout is surmised in the fig 1.
Generic solution
The survey conducted looked at all possible points of capture and concluded that the roof areas of
the recently constructed school buildings offer the best solution. The buildings are new and well
constructed and cover a large area they are also elevated from the ground giving necessary fall for
the water.
Other sources of rain water collection such as collecting from the road gulley’s using a Ram pump
system were rejected as the heavy use of paraquat in the area would make the water unusable.
This is also true of all systems which rely on ground water runoff.
Supply and demand
The most critical factor in designing a proposed solution is to identify what the water demand will
be. In this, clarification must be made as to the actual water usage is stated in Litres per person per
day. (L/p/d). WHO guidelines state the bare minimum is 7.5 L/p/d for consumption, basic hygiene
and laundry. However the consumption in the villages when water is available is much higher with
the Poverty reduction fund stating a figure of 40 L/p/d. A general consensus of agreement is that this
figure is high and as a measured consumption rate must be barred in mind that there is a lot of lost
water in the system.
http://www.who.int/water_sanitation_health/emergencies/qa/emergencies_qa5/en/
4. Notes:
• The village cistern systems were supplemented by household rainwater collection
• A distinction must be made between water and drinking water. Drinking water is to a higher
standard of sanitation and will require post processing after delivery.
• Demand figures must also take into account the expanding population figure given at 2.9%
per year.
In our deliberations we have developed an algorithm for water demand which is best shown
graphically as in Figure 2.
The supply shortfall is represented by the shaded area on the graph
Notes:
1. An increased demand has been shown for the dry season although this is theoretical.
2. Supply and consumption from the gravity feed (natural springs) cisterns was measured
during the rainy season. It is assumed that there will still be a supply during the dry season
although this figure is not known.
3. Inclusion for supplementary water capture by households, no accurate figures are available
but needed to be included in the algorithm.
4. All villages were asked in which months do the experience water shortages. This did vary
slightly but usually between 3 and 4 months of the year.
As we are providing a supplementary system (not a replacement) we have used a value of 20 L/p/d
Demand calculation
Q (Ʃvolume of water: litre) = n (number of people) x d (demand (20)) x d (number of days shortage)
Example:
Q = 304 x 20 x 90 = 547,200 Liters
5. Supply calculation
Our preliminary proposal is the use of rain water capture systems, this principal driving force for this
being the construction of school buildings in the target villages, some of which are still under
construction. The large roof is of the school buildings offer a good opportunity for rain water
harvesting.
Calculation:
The average rainfall in Nong het district is between 1500mm - 2000mm per annum (1.5m - 2m)
This however should be verified and the setting up of a rain gauge would be a good idea, this will
need to be measured over a one year period.
Assuming 10% losses from wash over.
Example:
Therefore a roof measuring 30m x 10m will be expected: 30 x 10 x 2 x 0.9 = 540 m³ (540,000 litres) of
water.
From the data gathered on site of the size of the roofs, it than therefore be calculated the difference
in the supply and demand this is represented in table 1.
From the above table it is conceivable that in the majority of cases the supply is complimentary to
demand. With a few exceptions, however the issue becomes the practicality on the size and number
of the tanks. I.E. storage of 540,000 litres of water will require 18 off 30,000 litre storage tanks, a
clearly impractical proposition. Following this study it must be decided what is the practical number
of tanks would be required for the target installation. To complement the shortfall on practical rain
water storage tanks a system of domestic systems be introduced.
6. The generic designs are based on the installation of a number of tanks. Short squat tanks are
preferred as these will fit easily under the eaves and allow 5° fall on the guttering. 5° is recommend
as a minimum which would entail a drop of 1.75 m over a 20 metre stretch meaning the positioning
of the tanks is also critical.
Ideally the larger the tank the better limited only by the height of the tank and the logistics of
shipping. See figs 3, 4 & 5
Fig 3
Fig 4
7. Fig 5
It is proposed that at least initially the units to be ‘stand alone’ with the rainwater capture tanks
feeding a single tap. Discussions were made on the possibility of linking up with the existing village
cisterns in the future and therefore this must be carried over into the initial design.
The outlet tap must be lower than the lowest point of the tank, this is not always possible with
exiting site configurations, in some cases a pump and a header tank will be needed.
Notes on tank installations:
1. Use of a ‘first flush’ diverter should be used, these are simple devices which use the first few
minutes of rainfall to ‘clean’ the roof surfaces, gutters and feeder pipes. They operate
automatically requiring o input aside from the flow of water. They come in a number of sizes
and designs the following is a typical unit. See fig 6
Fig 6
8. 2. Location of tanks
In addition of the critical consideration of the vertical location, the lateral location could also
be an issue. With the fall requirement of 5° the tank has to be located close to the gutter
drop to take into account for the drop requirement and the diverter. It is suggested that a
row of tanks on the ‘back side’ of the school buildings but leaving enough room to allow
natural light into the class rooms. Stacking the tanks at the ends of the building is also an
option however this becomes an issue with the fall. This can be circumvented by dropping
the gutter water into underground ‘carrier’ pipes. See Fig 7
Fig 7
3. Gutter maintenance
The most imperative issue with the installation of rain water harvesting systems is keeping
the gutters and drop pipes clean. This will mean the instigation of maintenance routines, a
thorough clean and check over prior to the rainy season should suffice in normal
circumstances however if the roof has a tendency to be covered in vegetation more regular
cleans will be necessary.
4. Guttering and carrier pipes
As part of the installation is a critical factor that the guttering, drop pipes and carriers should
be installed to the highest standards possible. This covers the standard of the guttering and
pipes and hangers. The new school buildings generally are recent constructions and in good
order. Also the wooden roof struts are made from local hardwood and make excellent fixing
points. The guttering supplies can also be extremely useful for the supplementary domestic
rain water capture. Careful attention must be made to taking the ‘tap point’ from the roof at
the ‘lowest’ point.
5. Tank sanitation and keeping water fresh
A priority consideration for water storage is the need to keep the water fresh, free from
algae growths, pathogens and stagnation. In general rain water which storage tanks and is
capture from buildings keep fresh for long periods. This is due to the water being captured
from ‘inert’ surfaces (particularly combined with a ‘first flush’ diverter, removing a good deal
of the organic matter). Secondly a ‘closed’ tank will stop a good deal of ingress of organic
matter, animals and insects (particularly mosquitoes). The tank lining material is also inert
and does not promote growth of pathogens.
This issue was a point of some discussion and it was concluded that some form of ‘agitator’
be included in the installation of the tanks. The purpose of this agitator will be to regularly
stir the water, averting the onset of stagnation. The agitator could be a stirrer powered from
a small motor or a small submersible pump. Either could be either mains or solar powered.
9. 6. Water filtration
As part of a more comprehensive water supply program the twelve target villages are
undertaking a water filtration program with Abundant Water. This is mentioned on this
report as consideration should be taken at the time of installation feed to the water
filtration system and the possible requirement for a pump and header tank
7. Shipping to site
The proposal is recommending the installation of large plastic rain water tank. There
advantage over construction concrete tanks on site is they arrive as a working unit. They can
be shipped to site on a the back of a truck and are relatively easy to dismount move and put
into position (three people can easily maneuver a 30,000 liter tank)
Houaydeua is the only village where shipping to site might be an issue
Fig 8
8. Installation base and coupling
Prior to the arrival of the tanks the site must be prepared. This essentially flattening the
ground that the tanks will sit on, a shallow sand base is also recommended, this will take up
the contours on the base so that no stress points are introduced. It is recommended that all
the tanks be linked together with a 4” pipe at the base. This will make the egress of water
much easier.
9. Linking with gravity feed spring water tanks
Although the agreement on site was the proposed systems be ‘stand alone’ it would be wise
to consider integration into the existing water system in a future phase of the project. For
this it will be a general requirement for the ‘lift’ of the water to be up to 200m, requiring as
single phase motor to produce a 20bar pressure. These are available and a power
consumption between 5 KW and 10 KW per pump be designated. Also the pipe and fittings
at the discharge end of the pump must be designed to withstand 20 bar pressure.
10. Housing clusters and domestic rain water capture systems
From the calculations we see that in many cases the demand outstrips supply and there is the issue
mentioned the actual number of tanks required will be impractical. At present crude domestic rain
water capture systems are installed in a number of households. The effectiveness of this can be
greatly increased by the use of effective guttering which will be supplied similar as that for the rain
water tanks. The scope and size of the domestic rain water harvesting again will be limited on
practical sizes. In deed there is scope for a number of houses to ‘cluster’ and use a central larger
storage tank.
Grey water
As part of the overall concept of water usage, re usage and water conservation the concept of grey
water should be mentioned. Grey water is the capture and use of ‘secondary water’ from non
polluting sources (showers and laundry: not latrines this is considered black water).
During the study it was noticed a large quantity of water escaping from the cisterns, especially
where the taps have been removed.
This water could be re used see Fig 9
Fig 9
Notes on Grey water:
1. By definition grey water is collected at the lowest point. Therefore it will always require a
pumping system.
2. Care must be taken as to collect directly from water source using piping or gulley’s
otherwise an issue with paraquat contamination might occur.
11. 3. Its usage lifetime is very short, normally if not used within 24 hours it should be considered
as black water. If being used for irrigation an instantaneous pumping system should be
considered.
Ram Pumps
Ram water pumps have been around for decades and are essentially a simple gravity powered
pumping system. The pump relies of a flow of water (such as a river or stream), the momentum of
the water operates a combination of two valves and a pressure chamber which pulses as the system
equalizes and unequalizes in cycles. Note: there is always waste water flow. The amount of water
which can be pumped is calculated from how much flow water there is and how high the water
needs to be pumped.
http://www.youtube.com/watch?v=qWqDurunnK8
Fig 10 & 11
