yes dont snort codeine, it needs to be consumed in order to be metabolised into its active metabolites.
Exactly, putting codeine up your nose is essentially pointless. It will just burn and drip down your throat tasting like crap.
As dread said, when the codeine passes through the liver, it is metabolised into morphine. The only effect you would get, would be from the codeine dripping down your throat and being ingested. At which point, you've probably made yourself feel 'urgh' and wasted a lot of the codeine.
As for evaporating the water off, to be left with crystallised codeine, either pour into a big flat dish and leave to evaporate naturally in 24-48 hours depending on how deep the solution is. Or put it in the Oven on a very low heat setting and leave the water to evaporate off. Though if your going to snort it, don't bother, just drink it.
I'm guessing if you snort it as well, with opiates in general giving a large boost in histamine and the onset of any drug being potentiated by nasal ingestion, you may get a very itchy shock. The codeine is metabolised into morphine in the liver, but I think for codeine to release histamine, it just has to be in your system.
Codeine is only ever good in powder, if you want to store it or don't like drinking the solution so crystallise it, crush it and stick it in capsules.