Natural gas may be purified by removing C3+ hydrocarbons and CO2 in respective one or more separation units to yield conditioned gas lower in C3+ hydrocarbons and CO2 in comparison to the un-conditioned natural gas. Notably, the feed gas need not be subjected to joule-thomson expansion and molecular sieve dehydration performed by conventional processes. Rather, any water-rich reject stream from the separation unit(s) is dried downstream with a smaller compressor and smaller molecular sieve or gas separation membrane dehydration unit before it may be re-injected deep underground or deep under the sea bed.