By Michelle Railey

A simple toilet tank conversion recycling gray water from handwashing to fill toilet tanks can result in significant savings of energy, water, and utility expenses.

Baseline Quarterly Savings:

$1,940,238.00

1,404,806.4 gallons of water

3,231 kilowatt hours

Lilly and Water: An Impressive Statistic with Room for Improvement

“In 2024, our facilities recycled or reused 290 billion liters of water, representing 97.5% of our total water demand.” (Sustainability at Lilly)

CBRE: Climate Transition Strategy for NetZero 2040

Maximizes Resource Efficiency (one of four stated pathways): water, electricity, money.

Reduces emissions by reducing electricity use. (Environmental Sustainability at CBRE)

Definition of Terms:

Gray water: waste water from gentle use and streams without fecal contamination; can be potable after some treatment

kWh: kilowatts per hour (1,000 watts of energy per hour)

Lilly: shorthand for Eli Lilly and Company and/or its Indianapolis campus

Purple water: recycled, reclaimed water that is non-potable but may contain some fecal contamination but suited for other uses before treatment, usually marked    by purple pipes; also called “purple pipe water”

WaterSense: appliances and fixtures (i.e. toilets) certified by the U.S. EPA WaterSense program

Benefits:

• 5,619,225.6 gallons of water saved per year, minimum.
• 12,924 kilowatt hours of electricity saved per year, minimum.
• $7,760,952 dollars saved per year, minimum.
• Advances progress towards goals set by client, Lilly.
• Advances progress towards goals set by CBRE.
• Increases goodwill towards both companies.
• Positive public relations with attractive publicity and social media opportunities.
• Can inspire other companies and households to make similar changes to conserve water, energy, and money.
• For some employees, this would increase their positive perception of their workplace.
• Because the equipment works best with foaming hand soap, additional money can be saved as, in general, foaming soap is less expensive per use.
• Easy to implement in phases; doesn’t require systemic changes to be synchronized in order to be useful (e.g. positive change can be accomplished per unit, one conversion and ten minutes at a time).

Challenges:

• Cost per toilet in equipment and labor.
• The sheer magnitude of the number of toilets on Lilly’s Indianapolis campus (or, if scaled, the number of toilets on both Lilly and CBRE facilities globally).
• May require internal education/public relations campaign to remind people that the water used for the tank-top sink is the same clean, potable water used in standard sinks and not “toilet water.”
• For each tank-top sink, soap will need to be included: it will need to be both unfragranced and foaming as other types of soap can damage the equipment. Additionally, paper towel dispensers within stalls would add to expense but make it easier for people to have a positive experience and also be important for people who use paper towels to open/close doors.

Note: It is not entirely clear whether CBRE or Lilly pays for utilities for Lilly’s Indianapolis World Headquarters. Placing these savings in context of Lilly’s finances is difficult as Lilly, in its latest SEC filing, does not separate Utilities Expenses from Operating and Administrative Expenses. See: Lilly 10-K Annual Report Filing

Basic Calculations Assuming Two Flushes of Toilet Per Worker Per Eight-Hour Workday*

To emphasize, the savings in gallons of water, in kilowatt hours, in dollars would be much higher. These calculations were made deliberately using the most conservative estimates.

The average American toilet uses 1.6 gallons per flush [1], leading to 3.2 gallons per employee per day or 16 gallons per five day work week.

The average of work days in a financial quarter is 60 days, meaning the average employee uses a low-end average of 960 gallons of water quarterly just to flush the toilet, not including washing hands or other water uses.

The lowest cost in Indianapolis for 960 gallons of water used by industrial and commercial entities is $2.05. [2]

The mean amount of electricity to provide, treat, and distribute water is about 2,300 kWh per million gallons, [3] or 2.208 kWh per 960 gallons.

The average price per kilowatt hour for industrial use in Indiana is 9.08 cents [4].

The average financial cost for electricity based on low-end estimates for each employee to flush a toilet twice per day for a business quarter of the year is 20.048 cents.

Eli Lilly and Co. has 13,456 employees in Indianapolis [5], which means:

12,917,760 gallons of water and 29,710.848 kWh of electricity used per quarter for flushing toilets, based on the above assumptions. Average cost, per quarter, for the water: $26,481,408. Average cost, per quarter, for electricity to serve the water: $2,697,744.99.

Total Minimal Price Per Quarter for Employees to Flush Twice Per Work Day? $29,179,152.99.

Annually: $116,716,611.96.

However:

Recycling handwashing water to flush toilets using sink-to-toilet tank systems can recycle about .73 gallons of water per use, conserving about .87 gallons of water every flush. [6]

In the above Lilly/CBRE scenario, this .87 gallon savings per use would be:

23,413.44 gallons of water saved per work day, ca. $49.997. (Quarterly: 1,404,806.4 gallons and ca. $2,999.82)

53.85 kWh of energy per work day, ca. $488.958. (Quarterly: 3,231 kWh and ca. $29,337.48)

Total Quarterly Savings: $1,940,238

Annual Savings: $7,760,952**

Notes:

[*] An average that considers three toilet flushes per woman and one per man (assuming a urinal is used otherwise). The real numbers are probably higher, considering for longer shifts and overtime, and humans probably using the restroom more often than an average of twice per work day, restrooms without urinals, etc. There is also here an argument to be made for waterless urinals but that’s beyond the scope of this improvement suggestion.

[1] The standard since the EPAct (Energy Policy Act) of 1992 which went into effect in 1994. Toilets manufactured between 1980 and 1992 can use 3.5 gallons or more per flush. Alliance for Water Efficiency. https://home-water-works.org/indoor-use/toilets

[1a] Newer toilets meeting EPA’s WaterSense criteria can use as little as 1.28 gallons per flush without significantly affecting performance. An argument could also be made here for using WaterSense rated toilets in new construction or when replacing older commodes. Many sink-toilet units combine both benefits: 1.28 gallons per flush and recycling sink water for the tank, resulting in a net water use per flush of 0.41 gallons, on average.

[2] This assumes only the first tiered level of pricing, not including treatment, service fees, or differences in pricing due to pipe sizes or government credits. The first tier only covers the first  750,000 gallons. “Industrial Metered Water Service,” Water Rate No. 5. Citizens Water/Citizens Energy, Indianapolis. https://www.citizensenergygroup.com/custom/specialpages/ratesridersdownload.aspx?dbfileid=798

[3] Absolute mean, a low-end generality not factoring in source (groundwater, surface, fresh, well), locality, power of pumps and treatment facilities, sizes of pumps, or government credits or tax write-offs for equipment. Multiple sources, but this one, although from 2015, used primarily: Young, Rachel. “A Survey of Energy Use in Water Companies.” White paper for ACEE, American Council for an Energy-Efficient Economy. June 2015. https://www.aceee.org/sites/default/files/water-company-energy-use.pdf

[4] As of May 2026, see chart at U.S. Energy Information Administration. https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a

[5] It is not clear from the source if this is or is not inclusive of contractors. It definitely would not include guests to buildings, which would also add to the total. See Eli Lilly, “Key Facts.” https://www.lilly.com/about/key-facts

[6] Standard U.S. faucets use a 2.2 gallon per minute flow rate. For a 20-second hand-wash without turning off the tap while lathering, the gallons used would be between 0.73 and 0.75 gallons. However, obviously, in this recommendation, water used per hand wash would be based on the sink on the back of the toilet. Calculating this is finicky as water flow in the use of these devices is based on the tank fill rate and water usage of the toilet. The number 0.73 gallons siphoned into the tank, saving 0.87 gallons seems like a reasonable estimate based on standard American toilet flushes and handwashing habits. Obviously, this number can be lower or, depending on plumbing and a number of other factors, much higher.

[**] I cannot stress enough that this figure is conservative to the point of very meaningful underestimation.