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Gravity Water

Lack of clean drinking water is a major problem in under-developed countries.  Surface water which has been polluted by man and animals is commonly used.  This is the source for diseases such as cholera, worms, typhoid, dysentery, diarrhea, etc.  Nursing the sick drains the resources, energy, and progress of the community.

Over 1,400 “gravity water systems” have been built in the Lowveld of South Africa, improving the water quality for 41,600 families.  The health of the family improves two weeks after the systems is installed. Water supplies must be protected from pollution and stored for future use.

Drilling rigs, pumps, engines, electricity, etc. are not available.  Therefore, manual labor and gravity must supply the required power.  Pictures are available of the actual construction of such a system. It is hoped that this information describing methods and procedures to develop and store clean water will assist in the construction of more systems.

Rainwater Catchment and Sand Filter

Rainwater Catchment System

Rainwater Catchment. Catching clean rain water is one of the most common and oldest methods for collecting safe drinking water. The illustration of a roof catchment system is only to show a 5000 liter cement storage tank that can be easily built with hand tools. Materials and instructions for building this tank are detailed in Bulletin 4.
Sand Filter. The water from many rivers and lakes is polluted. A modern purification system or a deep well supplies the best, clean, safe drinking water. However, families without safe drinking water must build their own system to improve the quality of the water they drink. The illustrated sand filter has limited capabilities but can improve the water quality. The low-cost cement storage tank that is described in Cement tanks below can be used as the tank for the sand filter.


Sand filtration system drawing

Capping and Developing Springs

Springs are the most reliable source of natural filtered water in rural areas. Like the desert oasis all peoples search for, settled by and protected their source of life – the spring. This natural water source also attracts animals who can pollute and destroy the spring. Once again the problem and solution are the same – protect the pure water supply by controlling its flow for consumption by man with the excess for animals and crop irrigation.

Spring Cap Box Drawing

A minimum flow of one liter per minute is needed for a viable water source. Excessive (uncontrollable) flows are self-cleaning and basically require a distribution network rather than the protection explained here.  This system is for the small community with labor its main resource.  If the flow is less than 15 liters per minute a reservoir is not required. However, it is always an advantage to have stored water for dry periods and for crop irrigation. Storage can be located where the water is required or used as a distribution point. See below: Cement tanks.

In all cases the spring area should be fenced and access controlled. An ideal spring would be located on a slope
steeper than one (1) meter per 50 meters.  If storage is planned, the top of the storage tank must be below the eye of the spring for gravity feed. If there is not a slope then a covered spring box must be constructed with cisterns and/or buried tanks next to the spring to protect the clean water from pollution and evaporation.

Tools required: spades, cement trowel, hack saw blade, hoe, water bucket.
Materials required: wood boards for a cement form; 25mm or 40mm plastic tube 2 meters long (saw cuts with hack saw blade 50mm apart on the section behind the dam or inside the spring box); 100mm plastic tube one meter long; coupling for 25 or 40inm plastic tubing or hose is required to connect the spring and tank; cement; stone; washed sand; and gravel.  For a small dam, a mixture of one part cement, two parts sand and two parts gravel is recommended.


Spring Box Cap #2

In preparing to cap a spring, the eye of the spring must be cleaned.  On a slope this can be done by digging a trench from the spring and allowing the water to flow.  Clean the eye of all foreign matter, mud, trash, etc. so that the water flows clean.  If a trench cannot be dug, the actual eye will have to be cleaned by hand.  Remove mud and trash with buckets or shovels.  If the spring is small, a notched plastic pipe can be laid in the trench behind a dam (1/3 meter high) constructed of small rocks and concrete to create a reservoir of water.  The reservoir of water behind the dam is filled with medium size rocks and covered with a plastic sheet.  The balance of the hole at the spring eye is covered (filled) with soil to seal and protect the spring.

The plastic pipe which is notched only before the dam will have a continuous flow of water.  The plastic sheet covering the spring eliminates most surface water from entering the reservoir.  Some experienced crews dig another trench for the dam and reservoir next to the spring eye eliminating the necessity of working in the water hole itself.  After the construction of the dam, the short distance between the prepared reservoir and the spring eye is opened to allow the flow through the prepared channel.  The old channel and spring is filled.

If the slope is very steep or the spring has a large flow, it may be necessary to build a spring box.  The spring box is made large enough to contain the eye of the spring with an open bottom (or back if on a steep hill).  Normally the spring box is a cube less than one meter by one meter by one meter. The walls of the box should be no larger than necessary and covered with a removable top to permit cleaning the box.  In this case a larger pipe is positioned to drain off the water during construction of the box and sealed or removed after the project is finished.  A smaller pipe of a size large enough to handle the flow of the spring is built into the box just above the drain pipe or bottom of the spring box.  To prevent contamination, a trench should be dug across the slope above the spring so that surface water does not enter the system.  Also pit latrines, dumps, etc., should not be located up hill above the eye of the spring.

Building a Cement Storage Tank

This procedure uses local materials to build a water tank manually.  Tanks can be built from corrugated steel, plastic, bricks, or masonry.  Cement (masonry) tanks using bricks or a reusable steel form are cheap, easy to construct and have a life of 20 to 30 years.  Large tanks need permanent brick sides with reinforced concrete coats inside and out to seal and strengthen the tank.  The 5000 liter reusable steel mold is best fitted in many locations.

Cement Storage Tank Fig. 4a

Cement Storage Tank Fig. 4b

Tools: Spades, trowels, hammer, screw drivers, wire cutter, pliers, hoes, buckets, shovel.

Reusable form – galvanized steel corrugated pipe (culvert) 1-1/2 meters in diameter, 2 meters long. The corrugated pipe is cut in half to form two half moons. The cut edges are reinforced with angle irons designed so that the pipe can be bolted or wired back together and collapsed inward for disassembly (see drawings for more detail).

Materials for a 5000 liter tank using permanent brick or reusable form –10 bags cement; 1 cubic meter sand; and 1/3 cubic meter gravel. Ratios recommended:

  1. For top and base — one part cement, two parts sand, and three parts gravel.
  2. For mortaring or plastering sides and interior of tank–one part cement and four parts sand. 50 x 1200 chicken wire fencing 6 meters long x 2 meters wide for reinforcing concrete;10 kg fencing wire 3.15 mm diameter (for burst strength); 1/2 KG binding wire 1.25mm diameter (for holding and fastening); 6.5mm x 200mm x 200mm concrete reinforcing mesh, 4 meters long and 2 meters wide (for reinforcing base and top).

Materials: 3 black plastic bags; wood plank (50mm x 300mm, 2 meters long); 100 meters of plastic pipe (25mm or 40mm diameter); 6 couplings (for 25mm or 40mm diameter plastic pipe); one 20mm tap (faucet); one 20mm galvanized steel pipe one meter long.

Construction- The top of the tank must be below the water level of the spring if the tank is to be gravity fed. A trench 1/2 meter deep should be dug from the spring to the location of the water tank. The tank area should be leveled. A square or round form at least 2-1/2 meters across and 1/4 meters thick can be constructed out of any material such as scrap wood or steel. The base is reinforced with mesh centered in the concrete. The trench (1/16 meter deep at this point)) ends in the center of the base. A plastic tube (the inlet) should extend up 1/4 meter above the concrete bottom of the tank. Another plastic tube should be positioned in the base before it is poured and should continue down the slope several meters from the tank (This is the overflow which supplies water for irrigation and animals.) After the tank is completed, a plastic coupling and tube is added to this overflow pipe to maintain the desired level in the tank. Provision should be made on the surface of the concrete base for the cast iron pipe outlet and tap at this time.

The same method can be used to produce a top. The empty cement paper bags are placed on level ground with a 5 meter piece of plastic tubing joined at the ends for a form. The reinforcing mesh should be laid on the plastic tube and paper bags and then cut to the size of the circle. The top should be as light as possible but strong enough to protect the tank.

A form, either reusable or permanent, is erected on the concrete base. A permanent form 1-1/2 meters in diameter and 2 meters high is made of half bricks with mortar between each layer and each brick. The vertical spaces between the bricks should not line up. The mortar should be allowed to set for two days. The outside of this brick form is then covered with chicken mesh wire. The fencing wire is looped around the first layer of bricks and twisted tightly together but not cut. The wire is then drawn continuously around each layer of brick to give the tank burst strength. Once again the 1:4 (cement to sand) concrete mix for plastering is prepared. To achieve the most uniform cement, the sand and the cement should be mixed dry before adding water. Be careful in adding water – it is a common mistake to add too much.

Concrete Top Fig. 4c

Complete mixing produces a good concrete plaster. If too much water is added, more sand and cement in the same proportions can be used to thicken the concrete. With the brick form both the inside and the outside can be coated (troweled on) with concrete the first day. (Thickness per coat should be approximately 20mm.) Be sure to trowel and work the concrete completely into the wire mesh. It is more important to get good penetration than a heavy coat on the first layer.

Therefore the first layer inside and outside should be very workable and not stiff. Two layers should be applied to both the inside and outside. The first layer on the inside should fill in the inside bottom corner of the tank and extend in part way to the center. The second layer on the inside should cover the inside wall and as much of the bottom as possible. These two inside coats seal the tank and make it waterproof. Each layer of concrete should be allowed to dry overnight. Two layers of concrete plaster should not exceed 35mm per side. It is good to introduce water into the tank as soon as possible to slow down curing; this increases the strength. Be sure that the inside coatings do not cover the overflow the inlet or the outlet pipes.


Cement Tanks Fig. 4d

In the case of the removable form, it is bolted or wired together on the concrete base. The vertical seams (cracks) in the form should be covered with plastic to insure that the concrete will not adhere to the form. The form and plastic is then covered with the chicken wire. The fencing wire is wound around the corrugated form with a wire in each corrugation to give burst strength. In this case, the concrete is troweled on the outside first (two layers with a maximum thickness of 20mm per layer). The form is then disassembled and lifted out of the tank. Two more layers are now troweled into the inside of the tank covering the bottom as before to make it waterproof. Total thickness of the tank should be approximately 75mm.

 

One day after the tank is completed, the spring tube in the trench can be coupled to the plastic inlet tube from the tank. The faucet should be connected to the galvanized pipe and the extension to the overflow pipe should be coupled to maintain the water at the maximum level. The tank will appear wet when water is first added. This is because the cement is curing.

Building a Reusable Form or Mold

Reusable Form Mold Drawing

Materials required – One galvanized corrugated pipe (culvert) 1-1/2 meters in diameter and 2 meters long; 4 angle irons 75mm, x 75mm, 2 meters long (with 10 equally spaced 10mm holes drilled in one side of the angle 62.5mm from the center edge of the angle iron); one 50mm x 150mm hard wood plank 2 meters long; (a) 40 bolts 5mm diameter 50mm long for bolting angle irons to steel pipe forms; (b) 10 bolts 10mm diameter 50mm long;  (c)10 bolts 10mm diameter 200mm long.  Note: If the two halves are secured together with wire, (b) and (c) can be eliminated.

Cut the pipe in half to create two half moons 2 meters long.  To each half of the steel pipe bolt to the inside a 75mm angle iron with the 10mm hole side pointing away from the culvert and even with the cut edge of the culvert.  The 50mm bolts should be equally spaced with 5mm holes drilled through the angle iron and the steel pipe where the corrugation touches the angle iron.  To the other cut edge of the steel pipe, the other angle iron should be bolted on the inside of the corrugated culvert the same as above but 50mm in from the edge with the vertical side of the angle nearest the edge.

To assemble the tank, wire or bolt (10mm x 50mm bolts) the sides with the angles next to the edge together.  On the side where the angles are inset 50mm, place the 50 x 150mm wood plank on the inside of the tank between the angles.  In this position the form will be separated 100mm.  The wall of the form and the wire or the bolts (10mm diameter x 200mm long) will hold the plank in place.  This method allows the form to be collapsed inward after the first two layers of cement are troweled on the outside.  Plastic is placed over the cracks where the form is bolted together to prevent the cement from bonding to the sides.