# Solubility of Lead in water from leaded pipes in Roman aqueducts

Lead can undergo the following reactions when cold and hard water passes over it: $$\ce{Pb^2+ + 2Cl- -> PbCl2}$$ $$\ce{Pb^2+ + SO4- -> PbSO4}$$

All these salts are sparingly soluble in water and have a tendency to stick to lead, rendering it passive and not allowing plumbosolvency to occur: $$\ce{2Pb + 2H2O + O2 -> 2Pb(OH)2}$$

My question is:

How did lead dissolve in the water flowing through the aqueducts if most of it's salts are sparingly soluble?

I have considered erosion of the salt layer formed on the surface but according to Wikipedia, the aqueducts had a very gentle slope

Vitruvius recommends a low gradient of not less than 1 in 4800 for the channel, presumably to prevent damage to the structure through erosion and water pressure. This value agrees well with the measured gradients of surviving masonry aqueducts. The gradient of the Pont du Gard is only 34 cm per km, descending only 17 m vertically in its entire length of 50 km (31 mi):

Wikipedia also has the following to say regarding lead concentration in the water:

Where lead pipes were used, a continuous water-flow and the inevitable deposition of water-borne minerals within the pipes somewhat reduced the water's contamination by soluble lead. Nevertheless, the level of lead in this water was 100 times higher than in local spring waters.

Any insights would be much appreciated!