This report summarizes the characteristics of small drinking water systems serving 10,000 or fewer people and how these characteristics may impact their short- and long-term sustainability. The report also provides information on ownership, operation, financial stability, infrastructure needs, and compliance with National Primary Drinking Water Regulations (NPDWRs). Additional analysis was conducted on community water systems (CWSs) serving a population of 500 or less since this particular subset of small systems appears to have the greatest challenges achieving capacity and complying with NPDWRs. Noncommunity water systems (NCWSs), which are not included in many of the national surveys that furnish data on water systems, are analyzed separately in Section 3. For the purposes of this report, very small systems are defined as those serving 500 or fewer people, small systems are defined as those serving 10,000 or fewer people, and large systems are defined as those serving greater than 10,000 people.