Thank you, Janie. I have thought about making my own ollas.
Maeve --I've been trying out terracotta pots for about 10 years. I thought I'd invented this system. The problem is that they are far too thick and the water doesn't seep through much at all. Haven't tried wine coolers but I think the same problem might occur.
The last link is an Australian site but the ollas don't seem to be available here.   I have a "wetpot irrigation system". They're made here. It's been good but I'd like individual larger ollas that I can hand fill. Like the ones pictured.
Cheers, Joy