Philadelphia's 10,000-acre Fairmount Park system is one of the largest such municipal spaces in the world. Yet the park's origins do not belong to any botanical benevolence.

Unlike Central Park - a deliberate attempt to preserve New York's dwindling green spaces amid urbanization - Fairmount began as a solution to a practical problem: providing Philadelphians with clean water.

In his vision of a new type of city marked as much by greenery as geometry, William Penn planted the seeds of five public squares. What is known today as Fairmount Park was not one of them.

In 1812, the city purchased the five acres of "Faire Mount" - the current site of the Philadelphia Museum of Art, and part of Penn's Springettsbury Manor - for the site of the future Water Works and reservoir.

It was primarily a sanitary effort, and consideration of recreational use of the space would not arise until the following decade. The South Garden, designed in 1829, is one of the oldest parts of the park, and one of the first public gardens in the United States.

The year 1844 marked the park's first expansion, with the purchase of the Lemon Hill estate, including its Federal-style mansion and 45 acres. Again, this was with an eye to protecting the water supply north of the Water Works.

The estate's previous owner, merchant Henry Pratt, would have perhaps approved of this civic-mindedness. His greenhouses - containing citrus trees, sugarcane, bananas, and other exotic plants - were open to the public during his lifetime. The official designation as Fairmount Park followed in 1855.

Park plans - like most nonmilitary activities - were put on hold during the Civil War, but quickly picked up once the conflict ended. Beginning in 1868, the park expanded onto the west bank of the Schuylkill.

Owing to its plentiful potables - as well as easy access to rail lines - Fairmount was selected as the site of America's first world fair: the 1876 Centennial Exhibition. More than 200 buildings were erected for the celebration, with nearly 10 million visitors - one-fifth of the total U.S. population - perambulating through the park.

David Johnston Kennedy was one of them. A Scotland-born immigrant who reached Philadelphia in the 1830s, Kennedy worked as a freight agent for the Reading Railroad. Yet this was only his day job. As an amateur artist, Kennedy produced more than a thousand watercolor paintings and drawings between 1840 and 1890, many of Fairmount. With these paintings, one may trace the park's shifting landscape - physical and natural - from its humble beginnings through its centennial splendor.

In Kennedy's brilliantly colored aquarelles are sights both familiar and strange to modern Fairmountaineers. Summer scenes depict children queuing up at the Popcorn Pavilion, while in another adolescents gather at their favorite bathing spot: a narrow stream with banks tall enough to prevent peeping.

Kennedy was a painter of all seasons, and his winter landscapes depict ice skaters skirting past one another in front of Boathouse Row, before the Schuylkill's pollution defeated the power of freezing.

The pleinairist also captured many of the structures put up for the Centennial Exhibition, of which all but one have been razed. In this, Kennedy's watercolors are not only pieces of art but also some of the only visual records of long-demolished buildings and public activities. The Historical Society of Pennsylvania holds the largest single collection of his work.

Kennedy formally exhibited his paintings only once: two landscapes, of Scotland and Ireland. He was working to collect and publish his Delaware Valley watercolors as "Lights and Shades of Other Days" up until his death in 1898.

Recent events in Flint, Mich., highlight the still-pressing issue of proper maintenance of a city's water supply, echoing the concerns of Fairmount's founders. However, these practical civic projects need not be unpleasant to the eye or nose, as the park's state today attests. Form may follow function, in parks and painting.

Join historian Elizabeth Milroy on Wednesday for "Counting Trees: The Search for Fairmount Park," part of HSP's free #SummerBookChats. To register, visit hsp.org/calendar.