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How do you figure out if a toilet is low-flow?

by LiveModern Webmaster last modified Jan 04, 2012 02:10 AM
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by last modified Feb 08, 2011

We are currently trying to reduce our water consumption in a 10 to 15 year old office building. One way is to possibly invest in a low-flow toilet system. But the existing system may already be low-flow... How do I figure this out? We are on a well, non-gravity fed.



Dear Kate,

In 1992, Congress passed the Energy Policy Act of 1992, which mandated that beginning in 1994 all residential and commercial toilets use no more than 1.6 gallons of water per flush. Therefore we can assume, based on the age of the building information you provided, that the toilets in your office building meet the 1.6 gallon-per-flush mandate.

However, I hate to make assumptions, because fact is always crazier than fiction and who knows what the building contractors actually installed. If you see no written indication on the base of the toilet, then lift off the tank lid and look inside for a stamp revealing the model number and hopefully the manufacturer's name. Contact the manufacturer and ask them what the flush volume is on your toilets.

However, don’t let the fact that you have 1.6 gallon toilets stop you from investigating additional water savings options with your toilets. To begin, do the toilets adequately clear the bowl after every flush? Many of the early low flow toilet releases skipped a step in R&D and performed poorly, requiring double flushing -- or worse, a readily available plunger for clogs. If your toilets do not consistently clear the bowl on a single flush, it is worth considering buying new units.

If replacing a toilet, consider a HET (high efficiency toilet). HETs come in two basic flushing volumes:

  • a dual flush, which typically uses 1.6 gallons per flush for solid waste and .9 gallons per flush for liquid waste, or
  • a single flush, which uses 1.28 gallon per flush.

Assuming you are on septic, you need to consider the distance between the septic tank and the location of a single flush HET. If the distance is significant (75 feet or more) and there is little or no assistance from gravity, the single-flush units may be challenged in delivering solid waste to the septic tank.

The next toilet characteristic to consider is noise. Some HETs are pressure-assisted (also called power-assisted or pump-assisted or vacuum-assisted) while others are gravity-assisted (also called wash-down). Pressure-assisted models are generally louder but leave a cleaner bowl than the wash-down models -- making pressure-assisted a good choice for an office building where maintenance costs come into play.

Lastly, to help you select the best toilet for your dollar, read the manufacturer’s specification sheet for the unit's Maximum Performance (MaP) score, which measures flushing performance. The EPA uses a MaP score of 350 as a baseline for HETs. For dependable service, I recommend you focus on models that have a MaP score of 1000. To see MaP test results for a wide variety of toilets, go to

If your toilets perform adequately but you are still interested in additional water savings, consider a dual-flush conversion kit. I have read up on a variety of conversion kits, but the HydroRight from MJSI, Inc., seems like it has the best performance potential -- plus it is very affordable and apparently easy to install.

For more information:

Read Green Home Guide's articles "Tips for Switching to High-Efficiency Toilets, Showerheads, and Faucets" and "5 Tips for Choosing a Low-Flow Toilet."




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