Don't Drink the Water -- Most hotels have their own clean water supply, or use filtered water, because of St. Petersburg's often bacteria-infected groundwater. It's a good idea to ask before brushing your teeth with tap water. Numerous brands of locally bottled spring water are good cheap sources of clean water. Some safe brands are Saint Springs (Svyatoi Istochnik) and Natalia. Make sure you ask for voda bez gaza -- literally, water without gas -- unless you want the carbonated kind.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.