Ahhhh.

So were not talking about a lot of water. How about a couple 55 gallon
plastic barrells, one for watering with a sump pump and a hose. That's what
I use in my basement where I grow my orchids only with a 12 gallon
container.

The second could have it's own sump pump and hose and be used for filling
the reservoir on the swamp cooler.

If the barrells are dark in color they will hold some heat for cool nights
and days.

I'd watch for sales for the pumps. You wouldn't need the expensive types.

Bob