The vendor has to undertake a survey for lead pipes before they sell the house these pipes should have been included in the survey.
I fear you may have to replace it. There are EU rules and probably French ones too. From Dec 25 of this year the permitted level of lead in water will drop to 10 micrograms per litre -- see this site http://www.developpement-durable.gouv.fr/L-eau-potable-et-les-canalisations,12971.html -- so at the very least you should get the level checked. I would go to the mairie and find out what's what. I know my son is having to rip out all the lead pipes he found in a house he bought.