The food they serve is fresh and very well prepared. I suggest not eating food from food vendors. Those are common-sense rules for traveling in any foreign country. Yes, it is safe to drink the water. Water quality is strictly controlled and monitored by the government.
Bottled water is readily available for worried visitors.
Spanish is the national language, but English is widely spoken, especially by people serving tourists. Tell us about the accommodations on your guided trip. We have traveled extensively in Costa Rica to find the best eco-lodges, small hotels and interesting inns. Everyone is assured of a private room and private bath with hot running water. As good eco-tourists, we select places that have a great regard for the environment, conservation and sustainable development.