If you are sticking to major towns, no. If you are going to remote beaches, Monteverde, or the Osa Peninsula, yes, the clearance is necessary for potholes and river crossings.

Is it safe to drink the tap water?

In most tourist areas, yes. If you are in very remote or rural jungle areas, carry a filtered water bottle.

Planning a Trip to Costa Rica: A Practical Strategy

Focus on two regions maximum to avoid spending your entire vacation in a car, as road travel is significantly slower than distances suggest. Rent a 4x4 vehicle if you plan to leave the main paved highways, and prioritize booking your arrival and departure logistics before filling in your daily activities.

Choose your two hubs. Pick one highland/volcano region (like La Fortuna or Monteverde) and one coastal region (like Manuel Antonio or Guanacaste). Trying to do the Caribbean and Pacific coasts in one week is too much driving.
Secure ground transport. If you are renting a car, book it 3 months in advance. Use a company that offers full insurance (CDW/LDW). If you prefer not to drive, book 'shared shuttles' (e.g., Interbus or Tropical Tours) which connect all major tourist hubs.
Route your arrival. Fly into San José (SJO) if you are heading to the central volcanoes or the Caribbean. Fly into Liberia (LIR) if your primary destination is the Guanacaste or Nicoya Peninsula beaches.
Book high-demand excursions. If you want to visit Manuel Antonio National Park or the Monteverde Cloud Forest reserves, buy your tickets online at least 2 weeks ahead. Daily entry caps are strictly enforced.

Do I need a 4x4?: If you are sticking to major towns, no. If you are going to remote beaches, Monteverde, or the Osa Peninsula, yes, the clearance is necessary for potholes and river crossings.
Is it safe to drink the tap water?: In most tourist areas, yes. If you are in very remote or rural jungle areas, carry a filtered water bottle.