| CONSTITUENT |
GUIDELINE VALUE (mg/L) |
MAXIMUM ACCEPTABLE VALUE (MAV) |
REMARKS |
| Total Solids |
500 |
1000 |
The total dissolved solids consist mainly of inorganic minerals. Excessive TDS levels affect taste.
Below 500 g/m the taste is usually good but water becomes increasingly unpalatable above 1000. |
| Turbidity |
1 NTU (<0.5 for
Giardia removal
by coagulation
and filtration |
10NTU |
Suspended matter causes cloudiness (turbidity). It is recorded as Nephelometric Turbidity units.
Excessive levels can protect micro-organisms from disinfection with chlorine and can be a source of
nutrients staining when washing fabrics. |
| Colour |
5 H |
10 H |
True colour is caused by dissolved coloured substances (apparent colour includes the effect of coloured turbidity). Colour is derived from decayed vegetation. It is measured in degreed Hazen. Excessive colour produces laundry and other staining. |
Substances
causing odour
and taste |
Inoffensive
to most
consumers |
Inoffensive
to most
consumers |
Tastes and odours have many sources such as fungal or algal growth, henolic substances (e.g. bitumen) or the effects of chlorination. |
pH
Expressed on pH Scale |
7.4 – 8.5 |
6.5 – 8.5 |
Low pH levels can cause corrosion of metals in the distribution system. A high pH will reduce the effectiveness of chlorine disinfection and can cause scaling problems. |
| Total hardness as CaCO |
80 |
200 |
Total hardness represents the calcium plus magnesium content. Excessive hardness can scale piping, heating elements etc and cause washing problems. Very low hardness levels can render water corrosive. |
| Calcium as CaCO |
See total
hardness |
See total
hardness |
Calcium is a component of total hardness Low levels can make waters corrosive but this effect is greatly influenced by other factors particularly pH, alkalinity and the presence of salts such chlorides or sulphate High levels cause scaling. |
Magnesium as
CaCO |
See total
hardness |
200 |
Magnesium is a component of total hardness. It is a laxative in the presence of sulphate (Epsom Salts). When over 250mg/L sulphate is present, the Magnesium content should not exceed about 30 |
| Sodium |
100 |
0.15 |
Sodium affects taste. Most users detect saltiness about 200mg/L. High levels
not suitable for young children or with some diets. |
| Aluminium |
|
|
Orally ingested aluminium is associated with Alzheimer’s disease, great care must be taken with some special medical applications such as kidney dialysis units. Aluminium compounds (e.g. alum) are commonly used for water purification |
| Silver |
|
|
Not hazardous at practical levels |
| Arsenic |
|
0.01 |
Most arsenic compounds are poisonous and generally enter water from timber preservatives |
| Lead |
|
0.01 |
Lead is most likely to be sourced from lead pipework with aggressive water (low pH or low hardness). |
| Iron |
0.1 |
1.0 |
Iron is common in bore waters or as a contaminant derived from the corrosion of steel pipes etc. Reddish-brown iron sediments cause discolouration of washing, stained basins etc, deposits and bacterial slime. High iron levels can affect taste and alter the colour of prepared drinks and food |
| Manganese |
0.05 |
0.5 |
Manganese is common in bore waters. It gives similar problems to iron, the deposits being black or dark brown. |
| Copper |
|
2.0 |
Copper in water rarely occurs naturally. It usually indicates corrosion of copper pipes or tanks. The levels encountered in drinking water are generally non-toxic to man. Above 5mg/L the water becomes blue and has bitter taste. Blue staining of fixtures is the usual indication of the presence of copper |
| Nitrate |
25 |
50
(as NO) |
Indicates contamination by fertilizers. Causes ‘blue baby’ problems (metahemoglobinemia) |
| Boron |
|
0.3 |
Low levels of Boron have been associated with testicular atrophy. Appreciable boron levels are
usually only found in deep bores |
| Chloride |
100 |
250 |
Chloride affects taste. Most users detect saltiness in the 200-300mg/L range. The guideline values are based on taste, not health hazards. High chloride levels make water corrosive. Chloride is a major component of sea water |
| Fluoride |
Recommended
range after addition 0.7 1.0 |
1.5 |
Fluoride is added to many supplies to promote dental health. The natural levels in NZ waters are mostly less than 0.2mg/L 1.0 Fluoride can damage teeth at high levels. |
| Sulphate |
50 |
400 |
Sulphate has a laxative effect at high concentrations, particularly in presence of magnesium. The guideline values are based on taste. High sulphate levels render waters corrosive |
| Sulphide |
Not detectable
to most
consumers |
|
Sulphide in the form of hydrogen sulphide can produce an unpleasant flavour in ground water devoid of oxygen. Levels as low as 0.5mg/L produce taste but the smell is evident at much lower levels. Sulphide can originate from geothermal activity or from the bacteriological reduction of other
sulphur compounds. |
Organic
compounds |
Many compounds
have individual
MAV levels |
|
Numerous organic compounds are found in water derived from both natural sources and pollution. Organic substances often affect flavour particularly after chlorination or are carcinogenic e.g. THM’s produced by the action of chlorine on natural organic compounds. |
| Zinc |
|
3.0 |
Zinc usually results from corrosion of galvanised or brass pipes etc as it rarely occurs naturally. It is not a human health hazard but may be poisonous to fish. Above 5mg/l may cause taste and cloudiness |
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