In 1987 the United State Geological Survey (USGS) installed a weir in the basement of the park administration building to measure how much water flows into the collection reservoir and another weir to measure how much water is not used and flows into Hot Springs Creek.
Now we can see data on exactly how much water is coming into the system to be used each day in bathhouses and drinking fountains. The USGS makes this information available on their website.
Before the weirs were installed, data on the amount of water produced by the hot springs was estimated by periodically draining the collection reservoir and recording how long it took to refill. Older park publications reflect an estimate of 850,000 gallons of water per day. Now we know that that estimate was too high because the current weir data shows around 700,000 gallons per day being collected into the reservoir for use by bathhouses and at drinking publics for the public.
The weir system only measures the amount of hot spring water that is part of the spring water collection system, water from the 27 most productive springs. This does not include the open display springs behind the Maurice Bathhouse, the Lamar and Noble Springs, or the Dripping Spring and Tunnel Springs at the Maurice Historic Spring display area. Like the aptly named Dripping Spring, there are other small springs that do not produce enough water to warrant the cost of collection for use. The water from these springs drains into storm drains and into Hot Springs Creek.
Why does the excess water flow into Hot Springs Creek? Before people began to divert the hot spring water into bathhouses, it naturally flowed into Hot Springs Creek. That is why water from all the open and display springs and excess water from the collection reservoir is allowed to flow into the creek.