Flood of filters on market

Publication: Daily Nation
Paper Date: Tue, Aug 20, 1996
Paper Page: 15
Byline: Terry Ally

Water pollutants

Ametryne ­ a pesticide found recently in tiny amounts in two Hampton wells in St. Philip

Atrazine ­ a pesticide used widely in the sugar cane industry is found in groundwater all over Barbados. High levels and prolonged exposure causes cancer. Levels are around 0.3 ­1µg/l*  and well below the American standard of 30 µg/l.

Chlorine ­ added in the well to kill any bacteria present

Nitrate ­ found in fertilisers and sewage. Levels are 6-8 mg/l**. The acceptable limit is 10 mg/l. High levels could deprive babies of oxygen. Boiling will not remove it.

Sulphate ­ found in fertiliser, causes discolouration in the water. About 27 mg/l at the Belle and 22 mg/l at Applewhaites. On the west coast levels are increasing but within the 500 mg/l limit

Bacteria ­ comes from sewage and is found only in agricultural wells which are used only for irrigation

Particulates ­ sediment, some of which may discolour the water. Top soil can be washed into wells during heavy downpours creating muddy water. This problem is generally associated with the Bowmanston well in St. John. The BWA monitors this and may stop pumping until the sediment settles, but by this time discoloured water would already be in the mains on the way to consumers.

* µg/ ­ microgram of pollutant in one litre of water.
** mg/l ­ milligrams of pollutant in one litre of water.

 

Barbados, which boasts a "pure" water supply, is being flooded with companies selling home water treatment systems. The salesman's gab often is that his product can filter out anything in the water ­ after all, the filter performs well in the United States!

What may work creditably in the USA may not necessarily work well in Barbados. That is because the types of pollutants in the American water system are different to those in Barbados, and actually vary from state to state. Barbados is tiny but pollutants also vary from coast to coast. In one part of Barbados, discoloured water may be a result of sulphate in the water but in another parish, it may be because top soil was washed into the aquifer. A major pollutant is nitrate which requires sophisticated and expensive treatment methods. A home water system is unlikely to remove nitrates from drinking water.

Before buying a water treatment system, then, it is important to know what the pollutants in the water are, and then ask the salesman whether they can be removed by his system.

The USA recently enacted a law which required that Americans be told what is in the water they drink. The law requires water companies to issue annual reports disclosing the chemicals and bacteria contained in tap water. The information must be written in simple language and sent along with the water bill to consumers. Such an open-information policy is not yet available in Barbados, but the Barbados Water Authority should be able to supply the information on request to concerned citizens.

Before buying a system request a copy of the manufacturer's Performance Data Sheet from which you can determine whether it is the right tool for the job.

What to know before you buy

BEFORE buying a system, you should know what types of filter it contains and what these filters can remove from the water. Following are the types of filters on the market:

Participate or Screen filters
     These filter grit, sediment, dust, rust, bacteria, and viruses from the water depending on the size of the screen.  Screens are measured in microns (1 micron = 0.0000394 inches).  A human hair is 80-90 microns in diameter, dust 0-5-7 microns, the smallest bacteria about 0.2 microns and the polio virus 0.009 microns. These screens are no good for removing soluble contaminants.

Activated Carbon Filters
     Activated carbon absorbs pesticides and many chemicals which cause an undesirable taste and odour in water, but is no good for removing inorganic contaminants such as nitrate. The carbon filter should be structured carbon blocked or granulated. Powdered carbon systems have proved to be ineffective and were not long-lasting.  It should also be combined with a particulate filter as water with a lot of particles could compromise the filter.

Reverse Osmosis
    One of the best all-round methods for removing a variety of contaminants such as sediments, bacteria, viruses and pesticides, but is no good for nitrate. The membranes can become clogged and must be replaced periodically. Low pressure, hard water and high iron levels in water can decrease effectiveness of some membrane.

Distillation
     Removes contaminants by boiling water and then condensing the purified stream into another reservoir. This removes bacteria and other contaminants, but may not be affective with pesticides and volatile organic chemicals. Also removes calcium which is prevalent in Barbados' water supply due to the coral rock. It produces "tasteless" water and will also remove useful minerals needed by the human body. 

Ultraviolet
    Destroys bacteria but may not remove all viruses and is not good for removal of most chemicals and will not work well with turbid (cloudy) water.

Ozonators
    These inject ozone in the water which kills bacteria and viruses and break down chemicals and pesticides, but there is no residual ozone left in the water and bacteria and viruses can grow after the treatment.

Ion Exchangers or Dieonizers
    Removes nitrates, sulphates, chlorides, iron, calcium and magnesium Deionisers may not remove nitrates very well if water supply is high on sulphates. Depending on the system used, chlorine which is added to kill bacteria, may be removed. Without any residual chlorine there is a danger that bacteria may enter and contaminate the water.

All filters (for particulate/screen, activated carbon, and reverse osmosis) must be regularly maintained because they can become saturated with chemical impurities and bacteria which may seep into the water.