Watson-Webb Sustainability Series: Watson-Webbites Flow Low
Something that students tend to complain about is the low water pressure in the dorms. This is particularly noticeable in the sinks, especially in comparing them to the sinks on the first floor. While it might follow logically that sinks with a lower flow would save more water, we need to take into account of the fact that it doesn’t take as long to wash your hands when there is a higher water pressure and water flow. This means people may be using the low-flow sinks for a longer amount of time. Therefore, I wondered how much water the low-flow sinks on our floor actually do save.
We measured water flow by running the sink for 10 seconds and measuring the amount of water with a Nalgene bottle with millimeter markings.
Figure A: Reading the water flow volume after 10 seconds on the 5th floor.
We did this for each of the four sinks on the fifth floor, and numbered the sinks in numerical order from right to left. We attempted to repeat the experiment on the two sinks on the first floor, but the water pressure was so high that water would begin to squirt out of the bottle before 10 seconds was up. Therefore, we adopted the use of a large tub to hold the water, for subsequent measurement with the Nalgene bottle.
Furthermore, the amount of water flow was so large for 10 seconds that we decided to decrease the time interval to 5 seconds, for sake of minimizing the environmental impact of our experiment and the convenience of measuring by a Nalgene bottle with limited capacity.
Figure B: Measuring large amounts of water flow by using a large tub to hold water, then measuring specific amount using smaller water bottles.
However, since 5 seconds is a shorter interval, which may magnify human error in measurement due to timing and turning the sink on and off. To compensate, we did two trials for these two sinks.
The data are found as follows:
Calculations: Unit water flow (mL/s) = Measured Water Flow (mL) / Time (s)
We also gathered data on one of the most common water-use activities in the dorm: hand-washing. Each member of our power group washed their hands as they normally do, and measured the amount of time it takes for them to do so. We each did this once on the fifth floor, to find the amount of time it takes to wash hands in a low-flow sink, and did so again on the first floor sinks to gather data in a high-flow sink setting.
Then, we calculated the amount of water that each member used based on the unit water flow calculations we obtained from measuring sink flow.
Calculation: Water Used (mL) = Time(s) * Unit water flow (mL/s)
(Rounded to 2 significant figures)
Based on the water flow data and calculations, I found that the flow rate for the 5th floor sinks is 141 ml/s, and that of the 1st floor sink is 846 ml/s. Conversions to the standard water flow rate unit of gallons per minute (gpm) can be found in the table below.
Calculation: Water flow (gpm) = Water flow (mL/s) *(1 gallon / 3 785.41178 ml) * (60s / 1 min)
I found out that the water flow of the high pressure sinks on the first floor is over 530% that of the fifth floor.
(2.3 gpm / 0.4 gpm) * 100 = 530%.
This is a significant difference in the amount of water that low-flow sinks can save.
To assess the relative water efficiency of the 5th floor sinks, I researched existing specifications for efficient bathroom faucets and found some through WaterSense. WaterSense is a partnership program sponsored by EPA with the goal of protecting the future of the U.S. water supply. They offer certification and labels for manufactures whose products meet EPA standards for water efficiency. The specification for bathroom sinks issued by the EPA is less than 1.5 gallons / minute. (WaterSense).
The low-flow sink water flow rates are 0.4 gallons per minute. This is significantly below the specification, which goes to show that these sinks are considered to be on the efficient end of water efficient sinks. In fact, the flow rate of the 5th floor sinks is 73% less than the EPA specifications.
Calculation: (1.5 gallons / minute - 0.4 gallons/ minute) / (1.5 gallons / minute) * 100 = 73%
WaterSense also specified that the Department of Energy uses 2.2 gallons per minute as the maximum flow rate standard for all faucets, as of 1992. Interestingly, the flow rate that we measured on the 1st floor sinks, 2.3 gpm, seems to exceed that amount by 0.1 gpm. This could easily be attributed to human error, however, this demonstrates that the water flow rate on the first floor is placed just at the maximum flow rate allowed for faucets.
This might be because the housekeeping staff fill up their water from the first floor, and that a high flow rate is required for increased efficiency of their work, as they don’t have to wait as long when filling up water for cleaning purposes.
In addition, the first floor bathroom is used most often by visitors of the building—friends, parents, workers, inspectors, and visitors of the university. It is evidently important that these visitors get a good impression for the dorm. Low water pressure may be frustrating to them or a sign of poor design. Infrequent visitors of the building tend to use the bathrooms on the first floor, and the designers wanted the visitors to have an optimal experience in the building, even if it means some compromises in the overall sustainability.
Based on the hand-washing times table, one can easily tell that the water used for hand washing on the first floor is significantly greater than the water used for hand washing on the third floor—over 3 times as much, in fact.
Everyone’s hand washing habits can differ significantly, so I investigated the amount of water that I would save by using low-flow sinks rather than the high-flow sinks.
I counted the number of times that I washed my hands in the past 24 hours in the dorm, and it amounted to 6 times.
I went on to determine the amount of water I would save by using only high-flow rates (like those on the first floor) and only sinks with low-flow rates (like those on the 5th floor.)
Water Use for Low-Flow Sinks
(7 times) (225.25 mL) = 1 576.75 mL
Water Use for High-Flow Sinks
(7times) (564 mL ) = 3 948 mL
Difference = 2 371.25 mL = 2.4 Liters
Low water flow sinks save 2.37 liters of water, per person, per day, just for the activity of hand-washing. This data is likely to be amplified for other people, because I am a water hippie and do not use very much water when I wash my hands (read on for more details about this.)
This is a significant amount of water saved. In fact, 2 liters of water is enough for a healthy human’s consumption per day (LennTech).
How much water do low-flow sinks is save in Watson Webb?
I wondered how much water Watson Webb saves in total from using low-flow water faucets, as opposed to the high-flow water faucets on the first floor.
Water wiki tells me the following information about average minutes of faucet use per person per day.
(Source: http://sogweb.sog.unc.edu/Water/index.php/Household_Water_Efficiency:_Faucets)
Note: The faucet use here includes water used for dish washing. Although the faucets are in a bathroom, they are the only sinks on our floors and residents do their dishes in these bathrooms using these sinks. Therefore, I believe it is an appropriate piece of data to be used to get a rough estimate water use in Watson Webb.
This data also reflects the fact that even though conserving faucet flow has a lower flow rate, people can tend to take longer time to do the same tasks than if they are using a high-flow sink.
Assuming the average minutes of faucet use per person per day on 5th floor to be that of the “conserving home,” and the same on the 1st floor faucet for the “non-conserving home,” I made the following calculations to determine amount of water saved.
[(15+8.9)/2 ] min * 0.4 gallons / min = 4.8 gallons per person
4.8 gallons/ person * 200 people = 960 gallons in the dorm
8.4 min * 2.3 gallons / min = 19 gallons per person
19 gallons / person * 200 people = 3800 gallons in the dorm
(19 gallons – 4.8 gallons) / 19 gallons * 100 = 75%
3800 gallons – 960 gallons = 2840 gallons
Using low flow sinks saves 75% of water compared to using high-flow sinks on the 1st floor. A difference of 2840 gallons per day is saved in the Watson-Webb are saved by adopting the low-flow sinks!