The large room on the north end of the building is the filter room, and it was constructed in 1895. It housed aluminum-bronze plates with many small holes in them. The plates were supported by a framework, and sand was placed on top of the plates. The water to be pressurized was poured on top of the sand. The holes in the plates were smaller than the sand grains so that only the water could pass through them. In this way, the water was filtered before it went to the pump systems. 

This room was constructed at an angle so it would fit between the water works facility and the superintendent's house.

Even with this filtration system, water supplied to Fort Collins was of poor quality when the water was muddy due to spring run-off or strong thunderstorms upriver. The Weekly Courier in April 1899 stated, "The filter at the water works pumping station was put to work on Wednesday sifting the saw logs, railroad ties, tree limbs, toads, wrigglers, and the thickest mud out of the river water before it goes into the pipes...."