No, tap water is not safe to drink. It is recommended to drink purified bottled water, which is available throughout the Dominican Republic. Hotels and restaurants use purified water to clean and cook their food and to make ice for their ice machines. Tourists are advised not to drink tap water.
People with sensitive stomachs are advised to use bottled water for brushing their teeth. Since you are travelling to a different ecological environment than the one your body is used to ingesting, the microbes in the Dominican Republic's water can affect some people very negatively. My hotel room at the Iberostar punta cana did have a three-prong plug, which I used for my computer. As far as the local water in Punta Cana is concerned, there are plenty of ideas for staying free of intestinal bugs while enjoying your holiday.
In Punta Cana, it is a safe place to visit, and you have the benefit of having extra police present when touring the tourist areas. The above data is made up of subjective, user-submitted opinions on water quality and pollution in Punta Cana, measured on a scale from 0% (lowest) to 100% (highest). To avoid iced drinks during your stay in Punta Cana, try the local concoction made by combining rum, red wine and honey, then steeping the mixture with tree bark and herbs. Most relevant to Punta Cana is the vaccine for hepatitis A, a liver disease often transmitted through contaminated food or water.
I didn't spend the night outside the resort, but I did explore Santo Domingo and the coastal town of El Cortecito in the Punta Cana region.