Do you have lid on your barrel?

Bird poo will add to the water some organic material for micro-organisms to get to work on. Warm water will do this process faster than colder and I would go for an underground store with a small pump. So long as you are not going to drink the water a tiny ammount, literally one or two drops, of bleach every week will likely solve your problem.

That's interesting Patrick! Stringing a copper wire along your roof ridge rids your tiles of moss build up, I guess it's the same principle.

Check out "The New Autonomous House" by Robert and Brenda Vale. Plenty of insights into using/storing rain water for a range of domestic uses.

Mark

Do you have a filter between the downpipe and the tank? For a filter I am using a tank filled with some sort of baked clay gravel - it is a pond filter that I picked up at the dump. This clay gravel is porous, and so has a big surface area available to bacteria. The bacteria eat the bird shit and whatever else comes down the downpipe. In a year or so, I have had no smells at all. I should also mention I have mesh over the top of the gutters to keep out moss, and just before the filter, I have a 'dead leg' for any sand or grit to fall into. I empty the dead leg every few weeks.

Good luck.