Kate, I'm no expert but any time you have 2 different metals in close proximity to each other there is going to be a reaction. Between steel and copper though, the majority of the galvanic corrosion will be with the steel.

There is an alternitive to pvc though. Research PEX pipe. It is a flexable hose type pipe that can freeze without breakage, something copper or pvc can't do. Hope it helps. Mark

Kate,

copper through concrete is a no-no. The copper will quickly degrade, ( 5-10 years and leak unless isolated from the concrete. Epoxy coatings have been tried, plastic sheaths have been tried, but the best solution is to use a dual plastic, metal reinforced product like IPEX. If you are hestitant about having you water move through a plastic, then using a PVC sheath over the copper, isolating it from the concrete, is your best alternate.

To avoid cracks in the concrete, there are several things that can be done. The first, is to weld the rebar rather than tie it. (Actually, you tie it in place, then weld it together). The second is to weld, ( or tie) pigwire, (eighth inch heavy wire grid) to the rebar, adding additional support for the concrete. The third, is to use fibre reinforced concrete in the pour, ( the fibers can range from steel pins, through fiberglass stands, to polyester pins). The fourth is to use a high PSI concrete, (6000 psi) rather than a low PSI concrete, (2000 psi). The fifth thing is to keep the concrete wet through out the entire cure cycle, so once the forms are stripped, cover the concrete with burlap or old sheets and keep those damp for the full 30 days of the concrete cure cycle.

The last thing that can be done to avoid water passing through the porous concrete is to use a product like Xypex to coat the inside of the tanks to water proof them.

What type of form are you using for this project? Have you looked into airformed concrete structures? I couldn't find the picture of it but I have seen a cistern that was made by spraying shotcrete on an airform.

Here is a link that might be useful: Monolithic Dome Institute