The water here IS safe to drink! Exceptions may be in VERY remote or rural areas, but unless you are way out in the boonies, you're OK.  Now if you are one of those with a seriously sensitive tummy... well then perhaps bottled water would be recommended.

Vacation travel and driving directions in Costa Rica can be confusing. Many foreigners are accustomed to road names and road signs, which are all but non-existent in Costa Rica.
When you are in a town or city, directions are explained with reference to a distance from a landmark. For instance, someone's house might be 300 metters south of the Church. Consider getting a GPS. Pricey but maybe makes you feel better.

Be very careful of petty theft like pickpockets, grab and run... etc. You are very unlikely to be the subject of a violent crime in Costa Rica, but you are always at risk for the small stuff. Don't carry your passport. Have a copy made of your front (picture) page and the entry stamp. The police here are cordial to tourists and unless you act like a jerk, all will accept that as a valid ID.

Now saying that... Never act like a jerk in Costa Rica.  Relax.  Enjoy this wonderful country and remember always you are a guest.  Things are different here, and not always the way you want them.  Foreign travel IS foreign and the Costa Rican culture is wonderful, but is very different from your home country.

Credit Cards. Use your credit card as much as possible for purchases as you will always get the correct exchange rate.  Use your ATM card if you need cash funds in colones. Don't do a cash advance thing unless you wanna pay silly interest rates. Now saying that... I have traveled extensively, and I believe Costa Rica is about the ONLY country that does not extort money when you exchange foreign currencies. There are exceptions (like at the San Jose airport!), but in general, you will be treated fairly.  Finally, and VERY important, TELL YOUR BANK you are going to CR. Tell your credit card companies too. Many will block your credit cards, especially for cash withdrawals. Also, set a realistic daily withdrawal limit that fits your needs.