…but not tested yet.
Last year I picked up some old wine barrels at a local winery with plans of turning them into a rain-water catchment system. I didn’t get around to the alterations until last weekend. They did get a little rain over the weekend, but not enough to put them fully to the test.
The rain-water flows into the barrels from the drainspout:

I put a little screen on the top of the barrel to avoid debris:

There are two barrels, linked by a hose at the bottom, so both barrels fill of the same drainspout:

The tap is on the second barrel (in the foreground). We did get enough water over the weekend to fill the barrels half-way:

But the real test will come when the barrels get completely full. I have installed a set of overflow hoses that drop back into the drainspout:

But I don’t know if they are at the right level yet, or whether they will leak. Only time will tell. The good news is that according to my calculations it should take less than 1/2 inch of rain to fill the barrels (55 Gallons each!).