by John Walsby
When we turn on a tap
we usually take it for granted that the water will be clean and
safe to drink but throughout much of the world there is a constant
danger that any fresh water will be contaminated by diseases and
toxic chemicals. When aid programmes are set up to help disadvantaged
people in Third World countries, one of the main needs is always
to improve both the quantity and quality of the drinking water
supply.
Where water is drawn
from wells or bores there is always a danger that the underground
reservoirs might be contaminated because of poor management of
both land and water resources by the same people that need the
clean water. In residential areas the effluent from septic tanks
seeps down and mixes with the groundwater and even where there
is mains sewerage there is a risk of fractured pipes and weeping
joints.
At vehicle service
stations the large steel tanks buried in the ground for safe bulk
storage of petrol and diesel quite frequently rust. Small but
steady fuel leaks can then contaminate the ground water.
From nearby industrial
areas chemical spills or careless disposal of solvents and other
wastes, frequently poison the soil and may drain down to the water
table. Chemicals also seep into underground water supplies from
rubbish tips, particularly those in gullies which also serve as
catchment basins for rainwater.
In the country agricultural
and horticultural pesticides and fertilisers leach through the
soil. Wherever people live, work and travel, there is a danger
of contamination. Water supplies that look crystal clear often
contain unwanted dissolved chemicals or organisms that cannot
be seen with the naked eye. Both can cause sickness and some can
cause serious illness.
Even in New Zealand's
remote areas where mountain stream water has always been regarded
as pure and palatable there is now a danger of infection from
a single celled micro-organism called giardia (Giardia intestinalis).
This protozoan animal thrives on food being digested in the guts
of people and other mammals. Its waste products interfere with
food absorption and frequently result in the host suffering from
diarrhoea, vomiting and body cramps.
The minute animal swims
freely about the intestine propelled by eight whip-like fibrils
called cilia. It absorbs the simple soluble food substances released
from complex foods by the hosts digestion and multiplies rapidly
by repeated division. They also produce ovoid cysts which pass
out with the hosts faeces to contaminate the vegetation and water
that other animals may eat and drink.
