Why not just leave the barrows as they are and siphon the water out when needed. You could take a length of garden hose and install an on/off valve at one end. When you want to use it just open the valve, insert the hose down into the barrow through the top opening, as far as it will go and then close the valve. Pull the hose up and over the side of the barrow and lower the valve end until it is lower than than the bottom of the barrow.
Open and close the valve to use the water. The garden hose will have to be twice the depth of the barrow plus a foot or so. Simple as that. Come winter just remove the hose. The hose could also be locked up and only inserted when water was needed.

That sounds like it will work. The bungs are solid. The flex makes positioning everything a little easier. For freeze protection I would dril a small hole in the now top of the drum for pressure release as the frozen water expands. Oh sorry I see you already called thst out. If you are worried about algae, i assume you have a translucent white drum. I have found spray paint to not hold up for more than a season. If you want to shade it, you have to do it with cladding of some sort.

Toolbelt - That is a great low tech solution though I am not sure it will work for us. Someone would have to be there every time it rained to switch the water from the drainpipe to a different barrel and then wait until it filled up and then switch it again. It doesn't rain all that often here but it would still be tough to make sure it happens. With the other design it all happens automatically. The whole system fills to capacity and then overflows. Plus because it doesn't rain that often here and when it does we get a large amount in a short time we need plenty of storage space (so lots of barrels). The manager is also talking about pressurizing the water eventually to allow it to be used for drip irrigation. I think it would all need to be joined together for this to work.

Nil. Thanks for letting me benefit from your experience. I am glad to hear the design with those materials is sound at least. I guess I will need 2 nipples per barrel to connect them in a series (more plumbing pieces to buy... oh well). I will keep the cladding in mind. We may grow an evergreen vine over them. That wouldn't be perfect but it would help.

Kate

Hello Kate,what do you think about dumping incoming water into a single large ( 11/2" to 4"depending on how many barrels are connected) pvc pipe running horizonaly above all barrels with tee at each barrel? To insure water is routed into empty or partly empty barrels without overflowinfg full one's,tee must extend 3" or more below overflow point. With brief and seldom down pour of rain you will catch more water than where water must travel through all barrels via 3/4tr hose before reaching last barrel. Each tee has window screen folded and stuffed around it to exclude skeeters and vent barrel as it fills/empties. I like the fact barrels sit on pallets leaving room underneath for plumbing. Rather than coupling barrels again at bottom,I prefer taping each individualy so that each can be emptied while others are full. Should a single barrel be punctured/spring a leak or vandalized,others will be uneffected. Barrel sits with bungs on top. Drill 1/2" hole in bottom. Alighning hole directly below large bung at top will make it easier to install short 1/2" mipt nipple. I like to size hole so that nipple is a snug/screw in fit. With a screw in fit,you will need a tool from hardware store desighned to remove/install sprinkler risers. While there,pick up "PLASTIC" retainer nuts with built in washers desighned to hold two handle facuets on sink. Apply silicone caulk to threads at one end of nipple then screw nuts on to leave 2 or more threads exposed on nipple. A thin bead of caulk formed as nut is screwed on is desirable. Lay assembly aside overnight to dry and lock nut in place. Apply generous bead of caulk to washer and screw exposed threads into a pipe with 1/2" fipt on it. Lower nipple through bung and begain screwing into hole. After nipple is well started and become's snug,apply caulk and install outside nut. With the help of riser tool and a wrench,you should be able to pull nipple tight with ease. The proper name for facuet which screws onto nipple is "boiler drain" meaning it has fipt. Freeze protection will be dramiticly inhanced by mounding compost material on pallet surronding lower 2" of ballel. Even more protected as compost cover's higher on barrel. Maintaine a cold compost pile next to barrels making it easy to replace material as it composts.srinks and sifts through gaps in pallets. Three things will happen to inhance freeze protection. #1 Lower extreme of barrel plus plumbing is insulated #2 Ground heat will rise below barrel #3 Heat generated by composting process adds to that from ground. The cherries on top are A. Unlike most composting efforts,aquireing, moving and managing material is done in small managiable bits of time and effort. B. At the exact same time of year majority of compost and mulch is needed in the garden, the area around barrels can use a sprucing up plus energy level of gardeners is at it's peak. Which brings us full circle to the ability to manage barrels individualy. After first barrel is empty,it and it's pallet are pulled offline to alow easier more thorough clean-up before pallet and barrel are reset. If a barrel is to be offline while possibility of rain exists,stuff rags,plastic trash bags or something in tee to prevent wasting water. I hope all that make;s sense because I made it up while a friend and I were consuming juice of what started off to be preserving berries in water and brewer's yeast. Same as any paint project,cleaness and prep is 90% of success. Apply pvc paint primer ( not to be confused with pvc cement primer) to plastic barrels before painting. Happy gardening.

Klem