Unfortunately, "lead in the water" is not a boolean, and is extremely dependent on things the landlord doesn't control - especially the chemistry of the municipal water supply. But our legal system makes it easiest to sue the landlord.
Sure, you could rip out all the old metal pipes and replace them with (say) PVC. Even handwaving the expense and issues of that - did you just replace "lead" with "microplastics"?
- so how much filtering, for which contaminants, should they have to do? How often should they have to re-test the (probably municipal) water supply, to verify that their filtering is doing the job? And how much will they mark up the price of water for their tenants, to cover the expenses of all their extra filtering and testing?
Sure, you could rip out all the old metal pipes and replace them with (say) PVC. Even handwaving the expense and issues of that - did you just replace "lead" with "microplastics"?