Annex C - Guidelines on water quality

Source: Guidelines for Drinking Water Quality, Vol. I World Health Organization Geneva, 1984

Table 1. Microbiological and biological quality

Organism	Unit	Guideline value	Remarks
I. Microbiological quality
A. Piped water supplies
A.1 Treated water entering the distribution system
faecal coliforms	number/100 ml	0	turbidity < 1 NTU: for disinfection with chlorine, pH preferably < 8.0: free chlorine residual 0.2-0.5mg/litre following 30 minutes (minimum) contact
coliform organisms	number/100 ml	0
A.2 Untreated water entering the distribution system
faecal coliforms	number/100 ml	0
coliform organisms	number/100 ml	0	in 98% of samples examined throughout the year - in the case of large supplies when sufficient samples are examined
coliform organisms	number 100 ml	3	in an occasional sample, but not in consecutive samples
A.3 Water in the distribution system
faecal coliforms	number/100 ml	0
coliform organisms	number/100 ml	0	in 95% of samples examined throughout the year - in the case of large supplies when sufficient samples are examined
coliform organisms	number/100 ml	3	in an occasional sample, but not in consecutive samples
B. Unpiped water supplies
faecal coliforms	number/100 ml	0
coliform organisms	number/100 ml	10	should not occur repeatedly: if occurrence is frequent and if sanitary protection cannot be improved, an alternative source must be found if possible
C. Bottled drinking-water
faecal coliforms	number/100 ml	0	source should be free from faecal contamination
coliform organisms	number/100 ml	0
D. Emergency water supplies
faecal coliforms	number/100 ml	0	advise public to boil water in case
coliform organisms	number/100 ml	0	of failure to meet guideline values
Enteroviruses	-	no guideline value set
II. Biological quality
protozoa (pathogenic)	-	no guideline value set
helminths (pathogenic)	-	no guideline value set
free-living organisms (algae, others)	-	no guideline value set

Table 2. Inorganic constituents of health significance

Constituent	Unit	Guideline value	Remarks
arsenic	mg/l	0.05
asbestos	-	no guideline value set
barium	-	no guideline value set
beryllium	-	no guideline value set
cadmium	mg/l	0.005
chromium	mg/I	0.05
cyanide	mg/l	0,1
fluoride	mg/l	1.5	natural or deliberately added: local or climatic conditions may necessitate adaptation
hardness	-	no health-related guideline value set
lead	mg/l	0.05
mercury	mg/l	0.001
nickel	-	no guideline value set
nitrate	mg/l (N)	10
nitrite	-	no guideline value set
selenium	mg/l	0.01
silver	-	no guideline value set
sodium	-	no guideline value set

Table 3. Organic constituents of health significance

Constituent	Unit	Guideline value	Remarks
aldrin and dieldrin	mg/l	0.03
benzene	mg/l	10a
benzo [a]pyrene	mg/l	0.01a
carbon tetrachloride	mg/l	3a	tentative guideline value b
chlordane	mg/l	0.3
chlorobenzenes	mg/l	no health-related guideline value set	odour threshold concentration between 0.1 and 3 mg/l
chloroform	mg/l	30a	disinfection efficiency must not be compromised when controlling chloroform content
chlorophenols	mg/l	no health-related guideline value set	odour threshold concentration 0.1 mg/l
2,4-D	mg/l	100c
DDT	mg/l	1
1,2-dichloroethane	mg/l	10a
1,1 -dichloroethened	mg/l	0.3a
heptachlor and heptachlor epoxide	mg/l	0.1
hexachlorobenzene	mg/l	0.01a
gamma-HCH (lindane)	mg/l	3
methoxychlor	mg/l	30
pentachlorophenol	mg/l	10
tetrachloroethened	mg/l	10a	tentative guideline valueb
trichloroethened	mg/l	30a	tentative guideline valueb
2,4.6-trichlorophenol	mg/l	10a,c	odour threshold concentration, 0.1 mg/I
trihalomethanes		no guideline value set	see chloroform

a These guideline values were computed from a conservative hypothetical mathematical model which cannot be experimentally verified and values should therefore be interpreted differently. Uncertainties involved may amount to two orders of magnitude (i.e., from 0.1 to 10 times the number).

^b When the available carcinogenicity data did not support a guideline value, but the compounds were judged to be of importance in drinking-water and guidance was considered essential, a tentative guideline value was set on the basis of the available health-related data.

^c May be detectable by taste and odour at lower concentrations.

^d These compounds were previously known as 1,1-dichloroethylene, tetrachloroethylene, and trichloroethylene, respectively.

Table 4. Aesthetic quality

Constituent or characteristic	Unit	Guideline value	Remarks
aluminium	mg/l	0.2
chloride	mg/I	250
chlorobenzenes and chlorophenols	-	no guideline value set	these compounds may affect taste arid odour
colour	true colour units (TCU)	15
copper	mg/l	1.0
detergents	-	no guideline value set	there should not be any foaming or taste and odour problems
hardness	mg/l (as CaCO3)	500
hydrogen sulfide	-	not detectable by consumers
iron	mg/l	0.3
manganese	mg/l	0.1
oxygen - dissolved	-	no guideline value set
pH	-	6.5-8.5
sodium	mg/l	200
solids - total dissolved	mg/l	1000
sulfate	mg/l	400
taste and odour	-	inoffensive to most consumers
temperature	-	no guideline value set
turbidity	nephelometric turbidity units (NTU)	5	preferably <1 for disinfection efficiency
zinc	mg/l	5.0

Table 5. Radioactive constituents

Constituent	Unit	Guideline value	Remarks
gross alpha activity	Bq/l	0.1	(a) If the levels are exceeded more detailed radionuclide analysis may be necessary. (b) Higher levels do not necessarily imply that the water is unsuitable for human consumption
gross beta activity	Bq/l	1