I can not find any information on this. I would assume that hypertufa made at home would be no more toxic then any other chunk of
concrete, perhaps less so. But I don't know if it would work.
My terra cotta pot ollas were not porous
enough.
I imagine that even if the hypertufa was a little too porous, it wouldn't matter much in a dry hot climate like mine. It should still be more efficient then watering on the surface, rather like a micro drip that wouldn't break down all the time. The only loss would be the self regulating of a terra cotta olla, but that is no great loss in a climate where it does not rain for weeks at a time; the water is usually wanted, and the olla wouldn't be filled in wet weather.
Or am I missing something?