Is the tap water safe to drink?

No. Not even for brushing teeth if you have a sensitive stomach. Use bottled water for everything.

Do I need to rent a car?

Not for a first trip. The highway is busy and parking in towns is difficult. Use private transfers and public colectivos instead.

Planning a Week on Mexico's Caribbean Coast

Stick to a single base in either Playa del Carmen or Akumal to minimize travel time and maximize relaxation. Dedicate three days to beach time, two days to cenotes and ruins, and two days for travel logistics and local exploration.

Pick your base. Stay in Playa del Carmen if you want nightlife and ferry access to Cozumel. Stay in Akumal or Puerto Morelos if you prefer a quieter, family-oriented vibe with easier access to cenotes.
Book private airport transfers. Do not rely on taxi haggling at Cancun International (CUN). Book a pre-paid private van transfer (e.g., USA Transfers or Canada Transfers) to your hotel to save at least $40 and two hours of stress.
Map your excursions. Limit yourself to one major activity per day. The heat and humidity are exhausting. Pair one morning of ruins (Chichén Itzá or Tulum) with a calm afternoon at a cenote.
Use public colectivos. For travel between towns, use the 'colectivos' (shared white vans). They run every 10 minutes along Highway 307. Fare is typically 40-60 pesos ($2–$3 USD) per person, paid in cash to the driver.

Is the tap water safe to drink?: No. Not even for brushing teeth if you have a sensitive stomach. Use bottled water for everything.
Do I need to rent a car?: Not for a first trip. The highway is busy and parking in towns is difficult. Use private transfers and public colectivos instead.