

The browser warning appears even for a cert issued by a non public CA you have told your browser to trust, and most browsers already enforce a 398 day limit, so unless you have cooperative users, you’re already (effectively) capped at 1 year of validity.
WaterSeer was initially somehow related to some part of UC Berkeley, rather than MIT.
You may be thinking of this device: https://www.cell.com/joule/fulltext/S2542-4351(20)30444-X
… Or the metal oxide framework predecessor to it, or the newer thing that uses some sort of gel.
I’m not aware of a commercial product based on this work.