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A low cost gutter technique

using waterproof

shade cloth

for use in

Rainwater Harvesting

 

 

 

 

Peter Morgan

 

March 1998

Updated for the Web 2002

 

 

 

Low cost gutter technique for use in rainwater harvesting

 

Many thousands of houses in the rural areas of Zimbabwe are now fitted with asbestos or iron sheet roofing which makes them ideal for the collection of rainwater for domestic use. However, very few of these are fitted with gutters and rainwater harvesting tanks. Currently there are moves within the NGOs and within government to make rainwater harvesting more popular as a way of gaining water for domestic use. The technique has particular relevance where ground water is not easily accessible and where hand pumps may be far away. However the method has a valid application anywhere in the country – arid, high rainfall, rural, urban. Work in Zimbabwe has already shown that even in the drier parts of the country, sufficient water can be harvested at clinics to cater for the water needs of the clinic and its visitors throughout the year. The use of rainwater harvesting tanks is being promoted by several NGOs both at the family level and at schools and clinics. An important use for rainwater harvesting may be at schools without adequate supplies of fresh water nearby, where the area of the roof is large and the potential for catching large amounts of water is great.

 

Whilst standard guttering is available for use on the market, very few homesteads in the rural areas seem to use it, possibly because of its cost. Consequently large amounts of rain water, which might otherwise be put to good use by families, is lost every year into the ground below the roof.

 

This manual describes a simple technique for making guttering most suitable for small houses fitted with asbestos or iron sheet roofing, although the technique could be adapted for larger roofs on institutions. The technique described in this manual uses plastic sheeting or canvas material, the most suitable being “waterproof shade cloth” which is resistant to degradation by the sun and thus has a longer life than ordinary plastic sheeting.

 

The use of this technique may be the first step along a path that the family follows to harvest water from the roof. Once the simple gutter is erected, the harvested water which runs to the end of the gutter and through a “down pipe” can at first be collected in drums and other containers. The next step will be to make a larger rainwater tank and there are many techniques available for making such a tank, which include using fired bricks, and ferrocement materials (wire and cement). The Blair Institute, Agritex, Zimbabwe Council of Churches, Christian Care and Mvuramanzi Trust are some organisations that are currently working in rainwater harvesting techniques. Commercially made corrugated iron and plastic water tanks are also available on the market, although these are more expensive.

 

The method of using “waterproof shade cloth” (which is available at some hardware stores and garden centres) involves cutting the waterproof shade cloth lengthwise to a suitable width. The cloth is sold in lengths of about 5 metres and widths of 1metre and 1.2 metres. The gutters can be made so the lower surface is horizontal with a down pipe placed at the central or end point. But the preferred method is to cut the shade cloth so that the lower surface of the final gutter slopes slightly from one end to the other. Rain water entering the gutter then flows towards the slightly lower end, entering a receptacle like a bucket with an outlet pipe fitted to the base. This pipe then carries the rain water to a suitable jar, tank or reservoir.

 

The diagrams below show how the cloth can be cut from standard shade cloth widths. For the horizontal gutters, a 1m width can be cut along the length in strips 33cm wide. This is like an economy cut. A greater length of gutter can be made from a standard sheet using a horizontal cut rather than a sloped cut. The sloped gutter is made by cutting a 1m width or 1.2m width in half along the length, then cutting as shown in the diagram so that the cloth is wider at one end than the other. This will lead to a gutter pouch which is sloped. The sloped gutter is less economical but makes a gutter which will carry water more efficiently to the outlet. The sloped gutter also reduces “pouching” of water after a rain – where water can remain standing for days. Leaves falling into the gutter are also flushed away more effectively in the sloped gutter.

 

After cutting the cloth, the next step involves stitching a fold along the length of the strip on each side. Each side is folded in about 25mm and stitched along the length with a sewing machine with thin nylon thread or strong polyester thread. Nylon thread is preferred. The stitching is positioned so that the fold makes a tube through which 2mm wire can be threaded through the entire length of the cloth on each side. It is these two lengths of wire threaded through each side of the cloth which support the gutter to the roof.

 

Two lengths of 2mm wire are then straightened and folded at the leading edge and then pushed through the “tubes” (hems) formed on each side of the length of shade cloth. About 0.25m wire should remain on either end of the gutter.

 

The roof is then prepared to accept the gutter. Using a small hand drill a series of 2mm or 2.5mm holes are drilled about 10mm from the lower edge of the roofing sheet (see diagram). Two holes 10mm apart are drilled in the “well” or lower side of each corrugation and a single hole drilled on the upper end of each corrugation. Whilst each upper and lower side can be drilled in this way, the drilling of every other corrugation is normally quite adequate.

 

The gutter is then fixed to the roof first by tying the 2mm wire along the length of one side of the sheet to the series of lower corrugations. Thin 1mm wire is used for tying. Short lengths of 1mm wire are folded, pushed through the shade cloth under the 2mm supporting wire and then through the two holes in the roofing sheet and twisted on top. The lower side of the gutter is tied up in this way along its entire length. The gutter therefore hangs from the lower corrugation about 10mm in. The shade cloth is then folded up and the upper 2mm wire is tied using thin 1mm wire to the upper end of each corrugation. The 1mm wire is threaded through the shade cloth under the 2mm supporting wire and through the single hole in the upper end of each corrugation. The 1mm wire is twisted to hold the 2mm wire in place. The shade cloth now forms a bag or pouch slung from the roof and supported by the two lengths of 2mm wire. Water from the roof will enter the pouch and run along it to the outlet.

 

One end of the gutter is now closed off (both ends are closed off if the down pipe is led out from the centre of the gutter). One suitable low cost way of doing this is to fit a used and cleaned 500ml oil tin into the end of the pouch/gutter and wire in position. On the horizontal gutter the down pipe can be fitted at the end of the gutter or in the middle as shown in the photo. The “tee piece” connecting the gutter with the down pipe can be made cheaply in the first instance by taking 3 used 500ml oil tins, which are suitably cut and stitched together with wire. Water caught by the roof will then run into the pouch of the gutter and pass through the tee piece and into a down pipe which leads it to the tank. The down pipe can be extended in the most suitable way so that it delivers water to the tank or drums. Any suitable tubing can be used for the down pipe – PVC, polyethylene pipe or even shade cloth stitched up and supported. A low cost “down pipe” can be made by taking a series of 500ml used oil cans, cutting out the ends with a tin opener and then wrapping them tightly in waterproof shade cloth which has been prepared in the same way as the gutter.

 

The simpler and more effective method is to make the gutter sloped so that water simply runs out of one end into a bucket which is suspended from the roof timber with a nail. The base of the bucket is drilled out and fitted with an outlet pipe. In the example described in this manual a 25mm polyethylene pipe connector is fitted through a hole made in the base of the bucket and held with hard setting putty. The rain water collected in the bucket is then led through a length of 25mm polyethylene pipe to a suitable jar or tank. In the case described here a 1 cu.m. ferrocement tank has been used to store water taken from the sloped gutter and a series of 80 litre plastic dust bins for storing water from the horizontal gutter.

 

This method has been used at the writer’s house for the past four rainy seasons and has worked well with the sloped gutter being preferred for reasons given above. Because the gutter pouch does not face directly against the sun, the amount of radiation falling on the material is reduced and this extends the life of the material. Even after four years of use, the pouch is still not leaking. Even if it did start to leak, the greater volume of water would still pass through the gutter to the down pipe.  The method is now being tested in South Africa and Kenya as well as Zimbabwe.

 

This method can also be made to work on thatched houses. But the water becomes stained. Also because the end of the thatch is uneven, “pouching” of the water (when water is left standing in depressed pockets of the pouch after the rains have ended) is more common. Some experimentation is required, but gutters of this type have successfully been fitted to quality thatched roofing.

 

A 5metre long gutter collecting water from a roof 5 metres deep will collect about 10 000 litres of water per year if the rainfall is 500mm/yr. Quite a lot of this 10 000 litres will be used during the rainy season itself, starting November and ending about March in Zimbabwe. It is very wise to allow the early rains to just flow to waste, so that the roof will be cleaned before the rainwater is stored. Leaves accumulating in the pouch should be cleaned out from time to time.

 

The secret of successful rainwater harvesting is to conserve the water that is stored by the end of March so that it will last for much of the remaining seven or eight months when rainfall is very low. This precious water is best used for drinking and cooking only. If a family of 6 persons consumes 3 litres of water each for 8 months this amounts to about 4 500 litres. However some light rain will fall periodically during the “dry season” to help top up the tank. Careful management of the use of water is essential. A lockable tap help reduce wasteage or tampering

 

The concept of rainwater harvesting is growing in Zimbabwe. It is a cost effective way of using water that falls on the family’s own property and is a good long term investment. The family can start with a single tank taking water from one side of a roof and then add to this later on. Tanks made of good fired bricks or ferrocement last for many decades. Permanent gutters can be added in place of the “plastic” shade cloth gutters described in this manual once they have reached the end of their life. By this time the value of collecting rainwater will have been learned. The writer expects to get at least 5 years service out of his shade cloth gutter and possibly more. Time will tell! With the water supply of the ‘city” becoming ever more suspect, greater reliance is being placed on consuming rain water  which is safe and pleasant to drink. In practice the writer and his family collects water from the jar and other containers which is carried to the kitchen in buckets and then passed through “candle filters” to ensure 100% purity and safety.

 

Peter Morgan

 

Harare

March 1998

Updated for Website April. 2002.

 

 

 

 


How to make the horizontal “low cost” gutter

 

Stage 1.

 

Measure the length of the roof to be rainwater harvested and cut the shade cloth to this length. Cut the cloth about 33cm wide. Thus for a 5m long roof the cloth should be cut about 5 metres long and 33cm wide. Three lengths can be made from a 1m wide sheet.

 

Stage 2.

 

Make a fold along both sides of the cloth 25mm from the edge. The fold is now stitched in place. This requires a sewing machine and strong thread, preferably nylon or strong polyester. The stitching is made so that the fold makes a tube through which supporting wire can be passed. Hand sticking will take time, but is also possible. A stapler can also be used.

 

 

Stage 3.

 

Straighten two lengths of 2mm galvanised steel wire about 0.5m longer than the cloth. Fold over the leading edge of each wire and push through the “tube” made on each side of the cloth. About 0.25m of wire should remain on either end of the gutter.

 

 

 

How to make the sloped “low cost” gutter

 

Stage 1.

Two 5m long gutters can be made with one 5m X 1.2m (or 5m X 1m) width of waterproof shade cloth. Where the 1.2m width is used each final gutter cloth will be 60 cm wide at one end and 40 cm wide at the other. Cut along the length in the place indicated in the diagram.

 

 

Stage 2.

 Make a fold along both sides of the cloth 25 mm from the edge. The fold is now stitched in place. This requires a sewing machine and strong thread, preferably nylon or strong polyester. The stitching is made so that the fold makes a tube through which supporting wire can be passed.

 

 

Stage 3.

Straighten two lengths of 2mm galvanised steel wire about 0.5m longer than the cloth. Fold over the leading edge of each wire and push through the “tube” made on each side of the cloth. About 0.25m of wire should remain on either end of the gutter.

 

 

Preparing the Roof

 

Stage 1.

 

Drill holes in lower end of roofing sheets. A set of 2mm or 2.5mm holes are drilled in the roofing sheets 10mm from the lower edge. Two holes 10mm apart are drilled in the “well” or lower side of each corrugation and a single hole drilled on the upper side of each corrugation. The drilling of every other corrugation appears to give the gutter sufficient support. The illustration below shows holes drilled in every corrugation which would be a stronger technique, but would take more time.

 

Stage 2.

 

Attaching gutter to roofing sheets.

This is done by wiring the 2mm wire supporting the pouch of the gutter through the drilled holes to the roofing sheets with thin 1mm wire. The position of the wires is shown in the diagram below. The lower 2mm wire is attached first throughout the length of the gutter, the 1mm wire being looped through the shade cloth and underneath the supporting 2mm wire and then through the two holes in the “well” of the roofing sheet. When this job is finished the gutter is folded up and the “upper” 2mm wire is attached to the upper part of the corrugations using 1mm to bind the two together. The upper part of the gutter is attached along its whole length. Care must be taken to ensure the cloth lies straight and is not twisted.

 

Stages in attaching “shade cloth gutter” to roofing sheets

 

 

 

 

 

 

 

Directing rainwater from the gutter to the storage tank

 

Experience has shown that for the horizontal gutter it is best to make a “tee piece’ and fit this half way along the gutter. Water is then directed down through the tee piece into a “down pipe” into the water storage tanks. In this case both ends of the gutter are blocked off with an end cap. These can be made with two cleaned 500ml oil cans wired in place.

 

The tee piece can be made of plastic pipe or once again with 500ml oil tins for a low cost approach. The diagram below shows how this can be made.

 

 

 

 

 

 

Directing water from the gutter into a “down pipe” via a bucket

 

This has been the more successful method used by the writer. As described earlier, a water outlet pipe is attached to the base of the bucket which directs water into a nearby ferrocement water jar. The bucket is suspended from the roof in such a way that water flowing from the gutter falls directly into it. The diagram below shows one possible arrangement. In the case being described here, in the writer’s home, the water jar is some distance from the gutter and during a period of good rainfall, a 25mm polyethylene pipe is used to connect the bucket with the jar.  The construction of the jar will be described in another manual. Normally however the rainwater tank will be close to the gutter as shown in the diagram below.

 

 

Maintenance

 

An important aspect of maintenance of the gutter system is to ensure that it is free of leaves and other matter which will obstruct the flow of water. If the shade cloth gutter becomes badly blocked the upper set of wire attachments should be undone and the pouch of the gutter allowed to fall down and free the trapped leaves etc and then be attached back to the upper corrugations of the roofing sheets. The sloped gutter is partly self-cleaning for small quantities of leaves. In this case the bucket should be cleaned from time to time. 

 

The shade cloth gutter was designed to last for several years but it will not be permanent. The stitching will also last longer if it made of strong material. However, the unit should provide several years of service. The oil cans described in this manual will certainly rust and need replacing after some time, but they can be replaced by more sturdy parts at any time. Those at the writers house are now about 4 years old and still working. They can easily be replaced. There is room for local innovation in the design of gutters, elbows and water carrying pipes. There are also many ways of making rainwater collecting vessels, cement jars and rainwater tanks. Normal plastic sheeting might also be used, but its life would be limited perhaps to a single season. It is worth trying. 

 

Rainwater harvesters are an excellent way in which good quality water can be collected at the home, at the school or at other institutions. What is important is that the precious water collected is managed carefully so that once the rainy season comes to and end, the collected rain water will last as long as possible during the months when rainfall is scarce or rain does not fall at all. 

 

 

 

Shade cloth guttering

on permanent roofing

 

 

Various types of system have been devised for this gutter technology. The outlet can be fitted to the end of the gutter but this tends to accumulate water in the pouch. A central water outlet is better as shown with full end caps being fitted at either end of the pouch. In this case, water is being stored in a series of plastic dustbins.

 

 

This photo shows a gutter cut so that the lower part of the pouch slopes down towards the outlet. Water runs freely down to one end. The water is trapped in a bucket slung from the roof and passes down a 25mm polyethylene pipe to the water tank. This method is simple and very effective at catching water from this type of gutter and directing it to the most convenient water containers (brick tanks, jars, plastic containers etc.) During a shower, water flowing from the end of the pipe might also be directed to a series of smaller containers.