Drinking water must be pure. The elimination of undesirable components such as organic matters and metallic trace elements with the aid of lime milk is an integral part of the water purification process.
Lime milk is also used for softening or remineralising drinking waters, in order to achieve a calco-carbonic balance in the water.

Remineralisation

When water is too soft (too acid), it can damage pipes. The application of lime neutralizes the corrosive action of the dissolved carbonic acid by transforming it into calcium, through this chemical reaction:
 

Remineralisation

H₂O + Ca(OH)₂ lime milk + 2O₂ -> Ca(HCO₃)₂ dissolved + H ₂O

Decarbonisation

When water is too hard, it forms scale and needs to be decarbonised through this chemical reaction:
 

Decarbonisation

Ca(OH)₂ lime milk + Ca(HCO₃)₂ dissolved -> 2CaCO₃ insoluble + 2 H₂O

pH correction

pH adjustment using lime milk is the most important use of lime in underground drinking water production. Lime is more effective than other alkaline products.

Many industries need large quantities of softened water. This is mainly important in cooling water for circuits and boilers, to prevent the formation of scale. Most process water preparation techniques include the addition of lime milk. By precipitating the bicarbonates dissolved in the water, this cost-effective treatment softens the water, restricting the formation of scale. The chemical reaction is:

Ca(HCO₃)₂ dissolved + Ca(OH)₂ -> 2CaCO₃ insoluble + 2 H₂O

NikiLime has developed special qualities of lime milks, particularly suited to decarbonisation.

Precipitation of heavy metals

The use of lime to adjust pH levels (by making them higher) can precipitate most heavy metals in the form of hydroxides.

Precipitation of phosphates and sulphates

When waste water contains phosphates and sulphates, lime makes it easier to precipitate them as well as the heavy metals, in the form of insoluble salts - Ca₃(PO₄)₂, CaSO₄ - that are easy to collect.

Flocculation

The coagulant action of lime neutralizes the negative charge on colloid particles contained in water. It also causes the flocculation of suspended impurities which makes decanting easier. Lime acts as the flocculating agent to which metallic salts and/or polymers can also be added.

Waste water purification separates out and concentrates the pollutants suspended in the water in the form of solid matter known as residual sludge. This sludge is a by-product which consists of organic and/or mineral matter, which can contain trace elements such as heavy metals.

Biological residual sludge contains organic material which can ferment and is a health hazard because it contains pathogens.