The Jones Falls became nothing more than an open cesspool that emptied into the Inner Harbor in the early 1800s. It was decided to build a reservoir upstream, outside of town and use conduit to carry drinking and fire fighting water to the public.

In 1858, work begins to increase the supply of water from the Jones Falls by building a dam. The reservoir to be created would be called Swann Lake, later to be renamed Lake Roland. A conduit would connect the reservoir to the Mount Royal Reservoir, and the water would flow by gravity through a 3-mile-long elliptical bricked tunnel. A Valve House was installed on top of the conduit and was originally known as the “Harper Waste Weir” (later to be referred to as “The Cross Keys Valve House”); and its construction would be completed in 1860. The Harper Waste Weir was located between Swann Lake and the Influent Gatehouse at the Hampden Reservoir. The Influent Gatehouse to the Hampden Reservoir pipe configuration was such that Swann Lake water could flow to the Mount Royal Reservoir or to the Hampden Reservoir. The Harper Waste Weir structure was one of three stone Greek Revival gatehouses to be built as part of the Baltimore’s City municipal water system along a conduit that would run from Swann Lake to Mount Royal Reservoir. The other two gatehouse structures (construction would be completed in 1862), being the effluent gatehouse at Swann Lake and the influent gatehouse to the Hampden Reservoir.

By doing this, the amount of natural water flow down the Jones Falls was impeded and this lack of flow created a worse  situation for Baltimore – the Jones Falls and the Harbor could not be flushed out on a regular basis (except during storms, which caused severe flooding).

The structure on the left is the original Waste Weir. The wooden portion was built later to hold alum, which was added to the water by hand.

This building still exists and has recently been added to Baltimore’s list of historic places.