Before we get into the details of the model, let’s look at the two general options we will be evaluating with it – displacement and replacement.

Displacement

Displacing water in your toilet’s tank is an easy, low-cost way to start saving water immediately.  You can accomplish this by using a product specifically manufactured for this purpose, like the “Toilet Tank Bank” depicted above, which saves 0.8 gallons per flush.  You can also employ a used plastic beverage bottle filled with sand or gravel to keep it submerged in the tank.  Or, as a friend said in a comment about my Facebook feed of Part 1 of this series…”I remember an ecology module in the 6^th grade suggested putting a brick in the tank for water displacement”.   Yup, that can work too.

Upcycling plastic bottles or bricks is definitely a green, no-cost way to go.  However, we think the Toilet Tank Bank is the better approach.  Practically speaking, it will take a challenging combination of bottles or bricks to equal or exceed the tank bank’s 0.8 gpf of displacement.  This could interfere with the toilet’s flapper function, causing leaking that far offsets any savings achieved. 

The Toilet Tank Bank will cost you about $2.  It is readily available from a wide range of e-tailers.  Watch the shipping charges…maybe you can add a low-flow showerhead or other water-conserving item to your order to reach the minimum purchase amount for free shipping and achieve goodness all the way around.

Replacement

From a water conservation perspective, toilets can be classified as good, better and best.  Efficient toilets labeled 1.6 gpf / 6.0 lpf are good compared to their 3.5 to 7.0 gpf predecessors.  High Efficiency Toilets, or HET’s, offer 20% better conservation at 1.28 gpf.  And Dual Flush HET’s offer the best water conservation with a 1.28 gpf flush option for solids, and a 0.8 gpf option for liquids. 

The Model

We’ve modeled some mitigation scenarios for the two 3.5 gpf toilets at our Sunset Avenue and Buckeye Street properties (see the figure below for scenarios and results).  If you have a Google account and would like to access this tool for your own scenario testing, just click on the figure to access it in Google Docs spreadsheet format.  Please be sure to follow the instructions in red that tell you how to save a copy before modifying the spreadsheet.  If you don’t have a Google account, you’ll need to set one up (self explanatory at www.google.com). 

Any difficulties? Contact us and we’ll get the spreadsheet to you by email.

If you are motivated to save as much water as possible, and you can afford to spend $300 or more per toilet, you should give serious consideration to a dual flush model.  As the spreadsheet shows, installing a dual flush high efficiency toilet will reduce the annual water consumption at our Buckeye Street residence by over 9,500 gallons.  This is almost 28% of our household’s total water consumption of 34,500 gallons per year! 

If cost and payback period considerations trump maximizing water conservation in your mind, and your inefficient toilet looks and works fine, a Toilet Tank Bank is a good mitigation option.  We installed one in the toilet in our home immediately after measuring its 3.5 gpf water consumption.  This simple, low-cost effort will reduce our average monthly household water consumption by 8% from approximately 3,000 gallons per month to 2,760 until we can research, decide upon and install a high efficiency toilet.

If you are planning to replace your toilet anyway and are pondering toilets of differing efficiency, you can use this model to do a comparative analysis.  Input the less efficient of the two toilets to be compared as “existing toilet data”, input the more efficient as “modified or new toilet data”, and input the difference in cost as “cost to modify or buy new toilet”.  The resulting calculations will tell you the comparative savings and payback period for choosing the more efficient toilet.

OK, enough toilet talk for this installment.  We hope you will tune in to Part 4 where we’ll summarize our research into specific models of high efficiency toilets, and tell you what the plan is for replacing our 3.5 gpf toilets.

Determining Flush Volume

If you live in a home that was built before The Energy Policy Act of 1992 (United States) took effect in 1994, and have not replaced your toilet, it probably has a wasteful flush volume ranging anywhere from 3.5 to 7.0 gallons per flush (gpf). 

If you don’t know the flush volume of your toilet, and you don’t see “1.6 GPF” printed right behind the seat on the bowl (along with the equivalent “6.0 LPF” for litres per flush), there is an easy way to determine it. 

You’ll need a gallon jug or bucket.  With that in hand, just follow the five easy steps at this link from the Marin Municipal Water District to determine your toilet’s gallons per flush (gpf).  Or, follow our step by step video below.

Checking for Leaks

Leak testing is as easy as coloring the water in your toilet’s tank with something safe like food coloring, waiting for a half hour, and then checking to make sure that none of the coloring has shown up in the toilet bowl.  See Toiletology 101 for more details on testing, significance of leaks, and how to fix them if you find them.  

Data for Our Toilets

• Phoenix Street Property – two 1.6 gpf toilets manufactured by VitrA, neither leak.
• Maple Street Property – two 1.6 gpf toilets, one manufactured by Fremont and one by VitrA, neither leak.
• Sunset Avenue Property – one very old toilet, brand obscure, measured flow = 3.5 gpf, does not leak.
• Buckeye Street Property (our residence) – one Crane toilet, 3.5 gpf, does not leak.

So now we’ve got the data we need to build a tool that will allow us to determine our current toilet water consumption, estimate water conservation associated with various modification/replacement scenarios, and calculate payback times. 

In Part 3, we’ll present and discuss this tool, and make it available for you to use for your own assessment.

Until then, it is worth reading and thinking about this piece on Peak Water from Twilight Earth.  It may increase your sense of urgency (pun intended) to tackle toilet efficiency and other water conservation measures, regardless of what we learn about projected payback times in Part 3.

Thanks gromgull for the cool toilet image.