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Water Hardness

What is water hardness?

Water hardness is an aesthetic quality of water and is caused mostly by the minerals calcium and magnesium but is classified or measured based on the level of concentration of calcium carbonate. The Aesthetic Values for Drinking Water Notice 2022 indicate a maximum guideline value of 200 mg/L.

What causes water hardness?

Water hardness happens because of certain minerals in the water. The main ones are calcium and magnesium, which come from rocks like limestone and chalk. These minerals get into the water naturally from the ground.

How hardness is measured is based on the following scale:

Water Hardness Scale

Classification

Total Hardness

(Ca & Mg as CaCO3) mg/L

Soft

0-17

Slightly Hard

17-60

Moderately Hard

60-120

Hard

120-180

Very Hard

Above 180

Water Hardness of Central Otago District Councils water supplies:

Supply Area

Total Hardness

mg/L

Cromwell/Bannockburn/

Lowburn/Pisa Moorings

Ranging from 52 and 119

Pisa Village Bore

Ranging from 113-130

Alexandra/Clyde

Ranging from 41-54

Roxburgh

Ranging from 34-43

Omakau/Ophir

Ranging from 23-50

Ranfurly

Ranging from 27-34

Naseby

Ranging from 16-17

Patearoa

Ranging from 13-28

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