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Bacteria
Public
water supplies in the UK are usually good. Bacteria do ocassionally
get into mains water but they are normally quite harmless. However,
there are very unpleasant bacteria such as E.Coli and Coliforms which
can cause upset stomachs, sickness and diarrhoea etc. Under certain
circumstances, Legionella Pneumophila can be found and this can lead
to Legionaires' disease which can be fatal.
Bacteria multiply by dividing into two every twenty minutes. Legionella multiplies at twice this rate to produce, eventually, pneumonia like symptoms and the human immune system is usually unable to cope with this. At present there is no specific antibiotic for Legionella so prevention is important.
Legionella can only be caught by inhaling infected water droplets (the "sneeze" principle) such as produced by a shower or spa bath. The bacteria only proliferate between 37 ºC and 55 ºC so hot water should be stored above 60ºC. Industrial cooling towers are a potential source of Legionella and should be treated and tested regularly. It is important that showerheads are disinfected/descaled regularly
Water
storage tanks
Occasionally, an unpleasant bacterium can establish itself, and
multiply, in a cold water storage tank. For this reason tanks should
be inspected and tested regularly and cleaned where necessary.
Tanks should conform to Schedule 2 (16) of the Water Supply (Water Fitting ) Regulations 1999, which replaces the Water Bye-laws. This says that tanks should have tight fitting lids, be insulated and have a screened overflow to prevent insects getting in.
Old galvanised steel tanks which have started to rust should be treated as soon as possible or be replaced as rusty areas are potential sites for bacteria to establish themselves. If structurally sound, steel tanks can often be lined and brought up to current standards. This is much cheaper than total tank replacement.
Cooling
Towers
Cooling towers are cheap to install and run. They are quite
efficient but unless treated regularly with biocides and kept clean,
they are potential sites for the proliferation of Legionella. Towers
can have a range of temperatures within, some of which are ideal for
Legionella to multiply.
Potable
water systems
When newly installed in offices, hospitals, nursing homes, public
buildings, factories etc. cold and hot water services and underground
water mains should be disinfected using a chlorine solution before use.
After chlorination and flushing out, samples are usually taken to test
for any or all of the following:
- Coliforms
- E. Coli
- Legionella Pneumophila
- Copper and lead
- Pseudomonas
Pipework
After installation, steel pipework can contain steel swarf, millscale,
grease, hemp etc. Unless these items are removed, they can cause problems
later. A chemical clean ("precommisson clean") is carried out
using a chemical cleaner which can contain detergent, dispersant, de-greaser
etc.
After cleaning, a corrosion inhibitor should be added and afterwards monitored regularly.
If there is a chilled water system as well, it may be necessary to add antifreeze to avoid frost damage in cold weather.
Chemicals
Many different chemicals can be used in water treatment. They
are usually blends of different basic chemicals prepared for a specific
job. Briefly, here are a few examples:
Corrosion inhibitors - used in central heating and chilled water systems.
Biocides - used for treating water systems where bacteria could establish themselves eg. cooling towers.
Disinfectants - such as sodium hypochlorite or chlorine dioxide or hydrogen peroxide.
Showerhead descalers/disinfectant - shower head cleaner
De-scalers - acid based chemicals used to de-scale systems, boilers etc.
Cleaners - used to clean new and established hot/cold water systems.
Equipment
There is an amazing variety of equipment available for water treatment
purposes. Some of the most popular items are listed below:
Water softeners - many different variations available, domestic and industrial. Once installed, they give very little trouble. They can save a lot of money in the long run by reducing soap usage and preventing scaling up of water heaters.
Automatic dosing - where treatment chemicals have to be added regularly to systems such as cooling towers etc. Their method of operation and control can be based upon various parameters such as pH, TDS., flow rate and timers. Automatic systems are usually designed and built for a specific application and they usually involve one or more small dosing pumps.
Pumps
- many and varied types and uses.
-
submersible pumps are invaluable when cleaning tanks.
- dosing pumps as above.
Ultra-violet irradiation units. Used in water systems to kill bacteria.
Filters - again, many and varied types and usage.
- activated carbon filters very useful for removing additives from potable water eg. chlorine and other materials that produce taste or odour problems.
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