Drowning is the number one cause of accidental death in children with Autism Spectrum Disorder (ASD). Few studies have examined the effectiveness of swim instruction for improving water safety skills in children with moderate to severe ASD. This study examines the feasibility and effectiveness of an aquatic therapy program on water safety and social skills in children with mild to severe ASD (n = 7). Water safety skills were evaluated using the Aquatics Skills Checklist and social skills were measured using the Social Skills Improvement Scale. We provide preliminary evidence that children with ASD can improve water safety skills (p = 0.0002), which are important for drowning prevention after only 8 h of intervention. However, social skills did not respond to intervention (p = 0.6409).