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Adding lime (Calcium Hydroxide) is a water softening process, and will remove carbonate (limestone or chalk aquifers) and non-carbonate hardness (normally from water passing through clay soils containing sulphate. It leads to the precipitation of calcium carbonate (1:1 moles), magnesium carbonate (2:1 moles) and, eventually, bicarbonate. Normally sodium carbonate (soda or soda ash) is added to remove the magnesium hydroxide, which is soluble in cold water (less soluble in hot water).

The addition of lime will raise the pH of the water, which will provide a disinfection action of itself. The WHO Water Guidelines state (table 7.6, pg 139) that up to 99% of Bacteria, 99.9% of viruses and 99% of protozoa present may be removed by the addition of lime through inactivation at high pH and removal from the water column by precipitative hardness. It should be noted that if chlorine is being used as a further disinfectant then it becomes progressively less effective as the pH rises, and should be generally no higher than 8.

It is difficult to tell why villagers would want the process carried out; I would be inclined to give them what they want as there are water quality benefits involved. I would also be inclined to talk to the villagers about why they think lime is required. It may be just because it has been carried out traditionally. In an emergency I would recommend going with what the population trusts, as long as you know it will not have any negative impacts. That way you can be sure that people are not accessing water in sufficient quantities because they are wary about the methods used to provide it. I may also have some benefit in conflict prevention; if you do something new and there is an negative impact, even if unconnected, the local population are likely to blame

Regards,

Cody