Traveling by bus there are two options

The public transportation system:

Transportes MEPE

Tel. (506) 2257-8129

Scheduled departures from San Jose:
6am, 10am, 1:30pm, 3:30pm.
The bus station is located inside Transportes Caribeños station,
Barrio Tournon, San Jose.

Using these instructions any taxi will take you to the bus station.
Approx. cost $5/pr each way.

This bus will drop you in Puerto Viejo.
From there you can take a taxi to Aguas Claras, Playa Chiquita.
Approx cost $7

The other is:

INTERBUS

(506) 2283-5573

interbus@costaricapass.com
www.interbusonline.com

They will pick you up at your hotel in San Jose and drop you off in Aguas Claras.
Approx. cost about $30/person one way.