I would agree with you on the lead or copper. I did not think about that I guess you would have to know whats in your local water.
However I don't have any issue with regenerating DI resin at all. I do separate the anions and cations. I save alot of money doing this I have a small amount of time in it.
There are plenty of DIY forums for this process and I have never had an issue.
I keep all types of corals, sps, zoanthids,
Lps and tge tds in my rodi water is always at zero until the resin runs out.
I am in the process of designing a degasser that will prevent the C02 from depleting the resin so quickly.