18 October 2007
To filter or not to filter
In the spirit of World Water Monitoring Day 18 October 2007, the Department
of Water Affairs and Forestry would like to stress that South Africa's tap
water is safe for drinking, particularly in cities and towns where there it
constantly complies with national standards.
It is thus the department's aim to keep water users informed about
effectiveness of some of the home filter systems which are touted by
salespersons as machines that purify tap water. What is the status of our
drinking water quality at present? But if we are to believe all that we are
told, we may be excused for thinking that it is not acceptable. At many
tradeshows or exhibitions salespeople of some home-purifications systems
(water-filters) promise to transform what they call "your highly contaminated"
tap water into pure and healthy drinking water. This is extremely misleading
most of the time.
A common demonstration involves placing two electrodes into the water and
applying a current across them. This you are told will cause the "contaminants"
in the water to drop out of solution. Within a few minutes brownish sediment
which appears in the water, the effect of which is both impressive and somewhat
alarming. The test is then repeated, this time using "pure water" (filtered
water) and in this case no sediment is formed. This is often enough to convince
one to purchase the filter to ensure that these "harmful" contaminants are
removed from the water.
However the answer is in fact quite simple. Good quality drinking water
contains minerals such as calcium and magnesium, which are most certainly not
harmful; in fact they are essential to good health. These minerals make the tap
water or mineral water a good conductor of electricity, so the current flows
through the water and the iron electrode actually starts to dissolve in the
water, causing brownish sediment to appear. The "pure water" is in fact
demineralised or distilled water and therefore is a very poor conductor of
electricity. When the current is applied, nothing happens, since no current can
flow through the demineralised water. This test therefore demonstrates the
presence of minerals in the water and not harmful contaminants at all.
Concerning the overall tap water quality
Much is being done to ensure that South Africa maintains its status as one
of the countries where one can safely consume tap water. This is the case for
the majority of reticulated water in this country especially in the cities and
bigger towns where the tap water constantly complies with our national
standards. While some of the rural areas are still a concern, huge improvements
are evident especially with government's commitment to supply all South
Africans with treated tap water.
For more information contact:
Leonardo Manus
Cell: 082 802 1005
Tel: 012 336 6511
Issued by: Department of Water Affairs and Forestry
18 October 2007
