What metal OK for RO water?

[banditpowdercoat]

OK, some may know I'm attempting to build a completely automated RO/DI water top off and membrane flush unit. BUT, I am wondering what metals are OK to come in contact with the RO? Most SOlenoids are Brass, but I have found some that are 304 Stainless Steel. I am needing a bunch of valve so cost is an issue. I have found, I think, a good source of 2 way valves, but I also need 3 way valves and have found some in 304SS. Is that gona hurt my water???