• Foundation diameter 2.2 m
• Outside Reservoir Diameter 1.72 m
• Inside reservoir diameter 1.42m
• Rebar Ring diameter 1.60 m → circumference = 5 m

The mason must wait 7 days before removing the inside steel mould and wait another 7 days to remove the top slab formwork (planks). Good planning is needed so that the mason:

1. Start with the reservoir slab & walls
2. Start the WP slab while waiting for the wall curing
3. Build the top slab
4. Finish the WP while waiting for the top slab curing
5. Remove the reservoir formwork

This reservoir design uses as little material as possible. This means that there is not a huge safety margin, the execution must be flawless. Pay special attention to the following points:

• This reservoir needs perfect curing, the pipeline with running water must reach the site before construction starts
• The inside form must be oiled with cooking oil as it will be in contact with drinking water
• The reservoir resistance to water pressure is mainly due to the rebar rings: take special care in the tying of the rebar and in opposing the horizontal iron ring connections
• The connection between bottom slab and wall is prone to leakage: create indentations in the slab and clean thoroughly before casting
• Fill the reservoir completely the day after casting and let it cure underwater for 7 days minimum

Before any mould reservoir construction, construction expert has filled the Format n° MF4-F62 “Water Point Configuration format”. This document is meant to help the contractor and supervisor to respect the following rules described in chapter 3 & 4:

Water inlet should have water going to the reservoir area (for concrete production) and the yield should be checked and above design minimum. The reservoir is made for 1 WP only (unless specified otherwise by design document), as close as possible to it: the elevation between the faucet of the water point and the slab of the reservoir should be above 50 cm.

Connect the overflow of the reservoir (⌀50) to the cattle through if the distance is less than 50 m. If not, build an erosion protection structure. For details about that structure consult Doc n° MF4-M15 “General construction standards” § Washout erosion protection structure.

It is better to place the 2 evacuations (reservoir overflow & WP evacuation) separately into the cattle trough wall rather than to use a Y.

To construct the foundation, follow the steps described in Doc n° MF4-M15 “General construction standards” § Structures foundation. During masonry construction, the inlet, outlet and overflow pipes have to be installed (masonry wall is 25cm thick, 40cm high and 220cm of outside diameter). They are simple PVC pipes with an elbow: ⌀50 for the overflow (that end with a coupling), inlet depending on the design (⌀32 or ⌀25) and outlet ⌀32. Installation dimensions are as follows:

When lean concrete is cast, care should be taken to maintain verticality of the 3 pipes. Before any concrete casting, protect the PVC pipes from entrance of foreign material with plastic bags, as follows:

To prepare the slab casting, rebar mesh has to be assembled. Use bent ⌀8mm rebar in a 15x15cm mesh, full diameter 157cm and the rebars must be bent to reach 40cm above the mesh. All bars must be tied together with iron wire and installed in the middle of the foundation on 2-3cm of gravel to maintain space below between the lean concrete and rebar:

After the rebar, the first level of the outside mould should be installed. This will be used as framework to cast the slab reservoir, all the bolts and nuts have to be present and tight. No rebar should touch the mould, distance is around 7cm between the bars and the mould:

All the dimensions and details can be found inside Drawings n° MF4-D50. Good practice standards about concrete handling and production can be found in Doc n° MF4-M13 “Concrete Handling and Production”. When rebar and mould are installed, 10cm thick slab can be cast with 1:2:3 concrete. The overflow coupling should be 2cm above the slab (to allow for finishing work):

After the casting, on the outer 15 cm of the slab make some deep cutting with the trowel to improve the future wall / slab connection.

The slab should be watered 2 times a day until the reservoir is filled with water. The mould can be removed after 24hours.

All the dimensions and details can be found inside Drawings n° MF4-D50. After removing the outside form of the mould and installing the inside form of the mould (1, 2 or 3 rings based on design), centred on the the slab (check distance from rebars around the slab ~7cm). All bolts are mandatory for a correct assembly of the mould, binding wire is forbidden. Oil the inside form with clean cooking oil (contact with drinking water):

Verticality of the inside mould must be checked with spirit level at 4 points, for every ring installed. Then vertical rebars ⌀6mm must be installed, fixed with wire on the already installed ⌀8mm slab rebars (every 15cm).

Then horizontal rebar ⌀6mm must be installed: cut 5.3m bars to bend and form a circle (1.6m diameter). Attach the 2 ends with 25cm overlap and place them outside the vertical rebar. The lower horizontal ring bar starts 5 cm above the slab.

See the chart below for the number of rebar circles needed:

Special care must be taken to tie the vertical and horizontal rebar with bending wire:

All the dimensions and details can be found inside Drawings n° MF4-D50. Good practice standards about concrete handling and production can be found in Doc n° MF4-M13. The entire wall must be cast in one day, so this step must start in the early morning to have a fresh mason and labour workers and enough the time to complete the whole wall.

The connection wall/slab is the most sensitive place to leakage, the slab has to be cleaned thoroughly with much water before installing the outside form of the mould:

Quantity of materials required for the casting of concrete for the reservoir per number of rings:

Reservoirs require specific gravel for concrete casting. Only small gravel should be used, no bigger than 15-20mm (and not 25mm as per Doc n° MF4-M13 “Concrete Handling and Production”).

The first ring of the outside form of the mould has to be placed centered on the slab (check distance from rebars around the slab ~7cm, wall thickness must be 15±3 cm all around). Level should be checked with spirit level at 4 points. All bolts are mandatory for a correct assembly of the mould, binding wire is forbidden. Oil the outside form with burnt oil:

Casting methodology:

① Cast the concrete: bucket by bucket, rotating around the mold (not all the concrete on the same side)

Vibrate a lot: the vibration teams follow the one who pours the concrete:

② with a 1/2” GI steel pipe inside the concrete,

③ by hitting the outside mold with a wooden hammer

④ by hitting the inside mold with a wooden hammer

When the first ring is completed, install the second outer formwork and continue casting (4 points spirit level check). All rings must be cast the same day. The day after casting the concrete, fill the reservoir up to the top with water for curing:

Let the concrete cure during 7 days minimum. To remove the inside mould, start to remove the door using a crow bar as gently as you can:

After removing the mould, the slab needs finishing work. Using mortar 1:3, create a layer above the slab, 2cm thick around the overflow PVC coupling and 3cm thick close to the wall by creating a slope toward the overflow. This finishing layer will protect the wall to slab connection for a better water-tightness and a better drainage when the washout is open.

All the dimensions and details can be found inside Drawings n° MF4-D50. Good practice standards about concrete handling and production can be found in Doc n° MF4-M13 “Concrete Handling and Production”.

A wooden formwork must be constructed to cast the top slab. The door must be installed above the washout pipe for handling purpose, details for door installation can be found here: Doc n° MF4-M15 “General construction standards” § Metal door installation.

A ⌀8mm 15x15cm rebar mesh 140cm in diameter must be installed 2-3cm above the formwork (use 2-3cm gravel) and tied with wire to the wall rebar. The slab is cast with 1:2:3 concrete, with slope toward the outside. Use the quantity of concrete described in chapter 7:

After casting, the slab should be watered 2 times a day at least for seven days and covered with jute bags or banana leaves. To finish the construction, adjust the PVC pipes length: outlet 3 cm above the slab, inlet 15 cm above the slab and overflow 5cm under the top slab.

If the reservoir washout is not connected to a cattle trough, a washout erosion protection structure must be cast following: Doc n° MF4-M15 “General construction standards” § Washout erosion protection structure.