Not in my opinion. There are little red taxis that are inexpensive and will take you all around Jaco. Most hotels will offer transportation services to and from the airport for a reasonable price.
Most hotels, restaurants and stores accept Visa and MasterCard; some accept American Express and other credit cards. In smaller towns, you may be charged extra to pay with a credit card.
We have found that every establishment we have been to in the Jaco area will accept US dollars If you want to exchange money you can exchange at the airport but the exchange rate is not favorable. Try and exchange currency at a local bank. You must have your passport to do this. If you must get colones at the airport, exchange the bare minimum and then head to a bank to exchange larger denominations. Airport taxi drivers will accept U.S. dollars.
The only water I would recommend drinking is water from a bottle. All restaurants will offer bottled water. I would also take it easy on the ice. I've never had an issue, but, do you want to risk it?