Background: Dental caries has significant public health implications afflicting young children. In addition to low social economic status, the most prominent risk factor for early childhood caries is sugar in the diet, particularly sugar-sweetened beverages. Dental treatment for caries in young children is commonly performed under general anesthesia and a significant proportion of children require repeated treatment. Interventions to reduce sugar-sweetened beverage consumption could lead to reduced rates of retreatment for dental caries in young children. Objective: This protocol describes the rationale, design, and methods of the “Thirsty for a Smile” feasibility study. The aim of the study is to assess the feasibility, acceptability, and appropriateness of a dietary intervention promoting water consumption in lieu of sugar-sweetened beverages among young patients, mostly from Latino heritage. Methods: This protocol describes a single-arm feasibility study. Twenty-one dyads of children and their caregivers will be recruited. Children between 2 and 9 years old who recently had treatment under general anesthesia for early childhood dental caries will be eligible to participate. The intervention has two components: (1) environmental, in which bottled water is delivered to participants’ homes; and (2) behavioral, in which caregivers will receive patient-centered counseling to increase children’s water intake and reduce sugar-sweetened beverages consumption. Dental caries and anthropometric data will be collected at examination during baseline and final visits. The primary outcome is feasibility and secondary outcomes are acceptability and appropriateness of the intervention. Results: Funding has been obtained from the National Institute of Dental and Craniofacial Research and the University of Washington approved the study. The feasibility study was conducted from March to November 2019. Conclusions: This feasibility study will test the study processes prior to a two-arm randomized controlled trial to determine feasibility and acceptability of the intervention and study procedures. This study may provide useful information for other researchers attempting to test similar interventions.