The underground brick dome water tank
Practical Action
The alternative offered by CWSSP was a handpump per 10 households. This still means walking
to collect water. Mrs. Emsayakar joked that they can still use the handpump of their neighbours
when they wish. She has not, however, had to do so yet as the harvested water meet all the
needs of the family of 5, as long as they conserve water carefully. She also said, however, that
she would prefer a piped / pumped supply which would mean that they could use as much water
as they wish.
Technical detail
The tank is a 5m3 below ground cylindrical brick construction based on the design of a Chinese
biogas digester (see Figure 2 below). It has a diameter of 2.5m and a height of 1.3m to the
base of the cover. The cover is a constructed using a clever brick dome design which can be left
open to provide access. Water extraction is either by bucket, by handpump or by gravity through
a pipe / tap arrangement where the topography and ground conditions are suitable. The cost of
the tank is in the region of Rps.6,500 (UK£100). The construction details given to local masons
are given below.
The Sri Lanka Brick Dome Tank – Construction details
Find suitable site
Dig pit 0.5m larger than the tank diameter
Plant an iron rod in the centre of the pit, making sure it is vertical.
Construct concrete base.
Start constructing walls using wire from iron rod to maintain the radius.
Once walls are complete backfill the gap between wall and pit with sand.
Make concrete ring beam to the shape shown. No reinforcing is required. Fit overflow pipe
at this point if required.
Prepare two wooden sticks – one end an ‘L’ shape and the other a ‘V’ shape. The length of
the stick is 2/3 that of the internal diameter of the tank.
Keeping the ‘L’ shaped end of
the stick to top of the tank
wall, place the ‘V’ end against
the iron rod and wrap string or
wire around the rod to support
the stick.
Start to build the dome shaped
roof of the tank with dry
bricks.
To start, stick the first brick to
the lintel with mortar and
support it with the first stick.
For the second brick, stick this
to the lintel and the first brick
and support it with the second
stick.
Push the third brick into place
(with mortar) next to the
second brick and move the
second stick to hold the third
brick.
Continue the process as with
brick 3 until the first course is
almost complete.
The final ‘key’ brick should be
Figure 2: The Tamana pump installed at Batalahena
Sri Lanka
shaped to fit tightly allowing
for the mortar.
Remove the sticks once the
first course is complete.
2