You will be amazed aty just how quickly wtare falling on a roof and down into a gutter and downspout will fill a 55 gallon barrel...
If you take a house that is like 40 feet long and 24 feet deep and collect the water from one side or the other of the roof it will take less than a an inch of rain to fill a 55 gallong drum to the top...
There are companies that offer kits and you might want to look intom them... You don't need much but you do need a valve at the bottom and and overflow flange and a screened inlet port for the top... I've rigged up a few with hardware store stuff but the kits are cheap and make the rain barrel very efficient...
Back in Wes Ginny I had a 350 gallon tank under my back deck where all the rain water from the back half of the roof went... It had an electric pump mounted on top and I had underground hose to my vaggie garden with an oscilator at the end and all I had to do was flick a switch and, wah-laa, the veggie garden would get watered... It was quite a system, not to mention a cool thing to show off...
We spent the day in the veggie garden today weeding, mulching (straw), suckering tomoato plants and side dressing everything that like lots of nitrogen... We have this guy who has a chicken farm and he calls us now and then when he has "the good stuff"... The good stuff is not only chicken litter but also composted dead chickens... Yeah, I know it sounds gross and it smells purdy bad but if is "the good stuff"...
(Dead chickens, Bobertz???)
Well, yeah... These chicken houses hold up to 100,000 chickens which grow from peeps to full grown in 45 days!!! Yeah, I know... It is unbelievable but the chicken you buy at the store was slaughtered before it was 2 months old... Anyway, if you bring in 100,000 peeps than there are gonna be a certain number that die from various reasons during the 45 days they are being grown and the state makes chicken farmers compost the dead chickens and so each chicken farm has that special compost areas where one day "the good stuff" is ready... I keep my pile way away from the house in the woods and take the tractor down there and scoop a bucket now and then for the veggies... Side dress them and it's... BINGO!!! They take off a'growin...
Anyway, today was the day so I reckon we are off an' running now...