International Conference on Rain Water Cistern Systems
USA - June 1982
3: Design, Cost, And Policy
Rain Water as a Water
Supply Source in Bermuda
Technical University of Nova Scotia, Canada
Any description of rain water supply systems in Bermuda must take into account
the geography and history of this small mid-Atlantic country.
The island of Bermuda is located at 32° north latitude, 65° west longitude,
917 km east of the North American coast. The "island" is actually a
. series of seven small islands, joined by bridges, that are the unsubmerged portion
of limestone deposits, approximately 100 m from the sea floor. The aeolean limestones,
laid down during glacial advances and retreats of the Pleistocene era, are loosely
cemented and extremely permeable. The rock is covered by a soil layer approximately
15 cm thick.
The island is 30 km long, with a mean width of approximately 1.5 km and.a maximum
width of 3 km. The total area is 53.1 km2. The elevation of most of the land mass
is less than 30 m above sea level, rising to a maximum of less than 100 m.
The climate is semitropical and frost free. Mean monthly temperatures approximate
20°C in winter and 30°C in summer. The average annual rainfall, based
on records since 1886, is 146.8 cm (Vatcher 1974); minimum and maximum 12-month
rainfalls are respectively 77.0 and 227.6 cm. Rainfall is fairly uniform during
the year, but onlthly average values for April through July are lower than the
One result of the high permeability of soil and rocks is the absence of freshwater
streams and lakes. Groundwater underlies 20% of the land area, in five lens. The
largest lens, with a mean thickness of 7.6 m, represents two thirds of the total
area. Brackish water (1-10% sea water) underlies another 23% of the island (Vatcher
Bermuda today is a self-governing British colony.
The island was uninhabited until its discover in 1503. It has been continuously
occupied since 1609, when it was settled by English colonists who also colonized
Massachusetts and Virginia in the United States.
The first Bermuda houses were similar to those in England, but construction
quickly adapted to indigenous materials of cedar and limestone. Native cedar was
in short supply as early as 1620, and stone buildings were encouraged, using cedar
for framing and trim. The native limestone, which can be cut with a saw and which
hardens on exposure to the atmosphere, was cut into blocks for walls. Roofs, supported
on cedar framing, were formed of overlapping limestone slates, 30.5 cm x 45.7
cm x approximately 3.8 cm. Limestone, burned in kilns, also provided the mortar
used to assemble both walls and roofs. This form of construction is basically
the same as that used today, except that concrete block walls have replaced limestone
in recent construction: in 1980, 95% of households lived in houses with outer
walls of limestone ("Bermuda stone") or cement block (Statistical Department
A unique feature of Bermuda roofs has been their role in water supply. Until
the 1930s, rain water provided the only source of potable water. Water was collected
on roofs, where wedge-shaped limestone "glides" were laid to form sloping
gutters on the roof surface, diverting rain water into vertical leaders and thence
into storage tanks.
Early storage tanks were rum puncheons or cisterns made of cedar. Others were
formed by excavation into rock and made tight with mortar. Prior to the 20th century,
tanks were located at the outside rear of dwellings, partly or entirely above
ground. Water was removed from tanks by bucket or hand pump and carried indoors.
In some later systems, hand pumps transferred water to elevated indoor storage
tanks. Current systems include storage tanks under buildings with electric pumps
and pneumatic tanks. Today, 96% of households are provided with piped indoor water
supplies (Statistical Department 1980).
Rain water was also collected from "artificial catches" created by
removing thin hillside soil and sealing the rock surface with mortar. Water from
large artificial catches continues to provide significant quantities of water,
e.g., an estimated 13.6 million l/yr from a catchment developed for a British
military installation, and 45.5 million l/yr from a catchment serving a major
hotel (Thomas 1980).
Roof water systems with adequate storage were not systematically encouraged
until the 20th century. Prior to adoption of current public health regulations
in 1951, storage capacities of 1400 to 22,000 l were common (previous public health
regulations required up to 6800 l per occupant, although 13,000 litres per occupant
were recommended), compared with typical storage today of 68,000.l.
Water was imported from North America during a five-year period from 1938 to
In 1932 a private company, Watlington Waterworks, began development of the
largest of the groundwater lenses, providing up to 3.5 million k/day of brackish
water for non-potable uses (primarily flushing) through a distribution system
serving the central part of the island. Part of this water fed a desalination
plant that provided potable water to several major tourist facilities. In 1979,
the Bermuda Public Works Department and Watlington Waterworks commenced a joint
venture aimed at rational development of the groundwater resource, involving new
wells in the central lens and delivery of potable water through. the Watlington
By the 1960s, desalination plants had been installed by several major hotels,
industry, and government. At present (June 1981) a government sea water distillation
plant is reaching the end of its useful life, and a brackish water reverse osmosis
plant is being brought on-line, by the Public Works Department.
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