In the early 1900s, which material did Philadelphia use to create a municipal water supply system?

In the early 1900s, Philadelphia utilized wood to construct its municipal water supply system. The use of wooden pipelines was a common practice during that time period because wood was readily available, relatively easy to work with, and provided a degree of flexibility in installation. Wooden pipes, often made from logs that were hollowed out, were used to transport water from natural sources to reservoirs and then throughout the city. This method was not only cost-effective but also aligned with the technologies and materials available during that era.

The other materials listed, such as plastic and metal, became more widely used in later years as technology advanced. Concrete also emerged as a popular choice for water systems but did so after the initial installations of wooden infrastructure in cities like Philadelphia. Thus, the historical context of the era supports the choice of wood as the correct answer.