Medical: The others answered this pretty well.
Water: Right, don't drink the tap water. Though I don't worry about things like icecubes from the restaurants. I drink and even cook with bottled water at my apartment.
Financial Transactions: I'm with Wells Fargo and I have found that only one group of ATM's here didn't accept my card. The weird thing is that I punched in the number of peso's I wanted and the machine just spit out my card with no message or warning. I had to stand there a few minutes just to make sure the machine wasn't going to make a winner out of the next guy in line. I found the ATM's outside of Lee Superplaza to work well.
If you want to avoid the ATM fee and withdrawal limits you can do a "cash advance" inside BDO (local bank.) They just run your card like a regular transaction and I got a great exchange rate. There was no fee other than maybe they took a slim slice off the exchange rate.
Difficulties and mistakes: The biggest problem I have run into here is telling the trikes where I want to go (many don't understand my English, so I have to take maps with me and point things out) and knowing how much to pay. They don't have meters.
There are a lot of things to know about how they work and I still don't have them down. For example, generally you can get to most places for 8 pesos unless you are going out of downtown and their only passenger. I can get to downtown from my place for 8 pesos but it costs 60 peso's to get back unless I catch a ride at a "terminal."
The other weird thing is the cell phones, which I still don't have totally figured out. I didn't really know what a sim card was before I got here and I buy "load" from the local sari-sari store. Load is basically for prepaid minutes or text messages.
So that is really the basics, transportation and communication. Getting a place to stay is pretty straight forward other than if you don't book ahead of time you will probably get a more expensive room than you had planned for. They never have the cheapest rooms available.
