Faraday to Jacob Herbert   28 February 1851

Royal Institution | 28 Feb 1851

My dear Sir

In reply to your letter of yesterday¹ containing the enquiry whether fresh water deposited in leaden cisterns is likely to obtain any quality rendering it prejudicial if used for culinary purposes or for drinking; I may state that there are cases where such injury has occurred & may occur. The liability is proportionate to the purity of the water in respects of Saline matter. Thus pure distilled water will act freely on lead - pure rain water will act sometimes - some spring waters are so pure that they act on the lead of pipes & cisterns. In thus acting they tend to coat the lead with an insoluble compound that serves more or less as a protection, and the protection is more perfect as the water is less pure in salts; especially of a certain kind. The consequence is that new lead cisterns & pipes injure such waters as act upon them more at first than afterwards - and again that a water which being not quite pure can be injured by a new cistern or pipe, ceases to be injured after some time[.]

The cases of injury in practice are not numerous, though they occur. The multitude of instances in which the water is not injured is manifest in London where leaden pipes & cisterns innumerable are properly & safely employed for the conveyance and retention of fresh water. Doubtful cases have to be examined each by itself²[.]

I am My dear Sir | Your faithful Servant | M. Faraday