Download Interpretation of

Interpretation of
Bacteriological
Results
1.
TOTAL COLIFORMS
The presence of coliform bacilli indicates general bacterial contamination of the supply,
whether of faecal origin or not. There are many types of coliform organisms, some
coming from the breakdown of animal matter, some from vegetable matter. If leaves,
even insects (eg Woodlice, spiders, etc.) can get into a catchment tank, then these will
affect the bacterial result.
Muck from animals, slurry pits, septic tanks and water drained from farmland where
animals graze will show heavy faecal pollution. Soils and rocks in North Pembrokeshire
are, unfortunately, not good at filtering out such organisms. Many boreholes (going
down 100 feet plus) are also consistently giving results showing coliform counts.
It is often the case that a figure of up to 5 total coliform (with no E.coli) can be improved
to a nil/nil result by carefully checking the system, eg. cementing cracks in source
catchment tanks or generally cleansing the system.
2.
E. COLI (Faecal coliform)
Escherichia coli is a natural inhabitant of the intestines. Sewage, cow dung, etc. will
contain millions of E.coli per 100 ml, but the number of pathogenic bacteria will normally
be relatively small. Water absolutely free of E.coli, indicates that there has been no
recent faecal contamination and therefore is likely to be free of all pathogenic bacteria
as well. Any E.coli in the water is a bad sign as it shows that it contains water that has
been polluted with excrement within the previous three days.
Drinking water containing E.coli is putting you at risk of having gastro-enteritis
(diarrhoea) and food poisoning-like symptoms. These microbiological tests give general
bacteria levels and indicate how wholesome the water is. Poor results could mean that
the water contains harmful viruses which could seriously damage your health.
To meet the drinking water standard there must be a Nil/Nil result:
Maximum admissible concentration – total coliform
Maximum admissible concentration – E.coli
=
=
0 (nil)
0 (nil)
P.T.O.
Compare these figures with your results
TOTAL
COLIFORMS
E. COLIFORMS
This shows gross pollution from all sources.
Pathogenic bacteria and viral infection is
180 +
180+
likely.
Gastro-enteritis
is
a
distinct
possibility unless water is properly treated.
E.coli similar in number to Total Coliform
indicates that pollution is from recent
70
70
animal (faecal) origin. Try and identify the
source to get a better result.
This often shows neglect or poor fitting
covers or a poorly constructed scheme. A
25
3
general improvement would probably get a
much better result.
Borehole results are often like this.
It is
taking some time (ie over a week) for water
35
0
to arrive at the source. If unable to improve
we would recommend a U V Light sterilizer
or other form of treatment.
Shows a reasonably good quality source.
Perhaps the odd insect or earthworm is
1
0
getting into the water. Check tank covers,
etc.
CM/MMB/03.03