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6 years ago, I needed to replace the main water shut off valve to my house. This required the city to turn off the water at the street. Incompetent city employee drives key through water pipe. Plumbers fix pipe, I realize that pipe is lead.

Yearly, the city (90% of which was built before 1950) sends out a water quality report, which reports undetectable amounts of lead. That is interesting since probably 90% of the city has lead pipe.

Several questions :

  1. How is lead pipe safe from leaching lead into water?

  2. Do cities usually treat the water to prevent lead from leaching into the water?

  3. What is the form of harmful lead (e.g. is it in aqueous solution, lead oxide, or forming ligands with some other molecule)?

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    $\begingroup$ Interesting fact: plumbers are called so because of the latin name for lead, plumbum. $\endgroup$
    – Gimelist
    Aug 24 '15 at 13:51
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In light of the recent events in Flint Michigan, this issue has come to the forefront (see this article from the American Chemical Society's Chemical & Engineering News and see this article). To summarize:

Active Measures to prevent lead corrosion:

  1. Maintain high pH. This makes lead carbonates less soluble in water.
  2. Add orthophosphates which create relatively insoluble layer on the inside of the pipes.

Without these treatments, the addition of chloride disinfectants aggravates the corrosion problem by forming lead (II) chlorides (which is water soluble).

As mentioned by Jaroslav, the time that water sits in the system also plays a factor.

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Lead pips are a common problem. Usually, it is safe to drink water from it.

So long as water is flowing, there will not be unsafe (or even detectable) levels of lead in the water. - True remark by @Some_Guy.

The problems accrue when the pipeline is not used for longer time. The lead concentration arises and can reach harmful levels. There is a possibility to install filters to remove lead from the water. This site is quite useful and provide more information.

  1. Lead is contaminating water if the pipeline is made of lead.
  2. I am not aware of any method that can prevent lead leaching.
  3. Over longer time oxides can be formed:

$\ce{2Pb(s) + O2(g) + 2H2O(l) -> 2 Pb(OH)2(s)}$

and other:

$\ce{PbCO3}$ or $\ce{Pb(CO3)2^2-}$

Elementary lead does not dissolve in water under normal conditions. Lead compounds are generally soluble in soft, slightly acidic water. Lead binds to sulphur ($\ce{S2-}$), or to phosphor ($\ce{PO4^3-}$). Reference here.

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    $\begingroup$ The key point here is that, so long as water is flowing, there will not be unsafe (or even detectable) levels of lead in the water. I can't speak for where OP lives, but in my area, anywhere that has lead piping has a periodic test for lead, and it never comes up positive. $\endgroup$
    – Some_Guy
    Aug 20 '15 at 14:49
  • $\begingroup$ That right. I will update the answer. $\endgroup$ Aug 20 '15 at 14:50

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