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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Jul 22

The Facts about Flushing

Posted on July 22, 2015 at 2:59 PM by Ann Vallee

by Dan Carney, Water Conservation Manager

Did you ever wonder where the modern flush toilet originated? The invention of the gravity flush toilet is attributed to Sir John Harrington, who in 1596 installed the first one in Richmond Palace for his godmother, Queen Elizabeth I. It required 7½ gallons for every flush, and it was advertised that during times of water scarcity 20 people could use it between flushes. Indeed, a porcelain throne!

After centuries of engineering improvements, today’s flushing toilets use a mere 1.28 gallons or less per flush. These modern marvels go by a variety of names including high-efficiency, ultra-high-efficiency, and premium-efficiency. Single-flush, tank-type toilets are the most common, although dual-flush and pressure-assist types are also popular.

Studies in the U.S. and Canada have shown the new generation of high-efficiency toilets to be reliable water savers, due in large part to the rigorous testing standards manufacturers are required to meet before a toilet can acquire the coveted U.S. EPA WaterSense label. The WaterSense label conveys both high efficiency and excellent flushing performance. Although California now requires all toilets sold/installed be high-efficiency, not all high-efficiency toilets are WaterSense-labeled.

There are thousands of high-efficiency (1.28 gallons per flush or less) WaterSense-labeled models for you to choose from. Some models—known as “ultra-high-efficiency” or “premium-efficiency” —use just 1.1 gallons or less per flush.

According to the EPA, a drainline study conducted in 2004 showed that toilets using as little as 1 gallon per flush did not cause clogging problems, depending on the condition of the plumbing in your home. This study also concluded that higher-priced toilets did not necessarily provide better flushing performance. Instead, look for the Maximum Performance (MaP) score of the model you’re interested in. The scores range from 350 to 1,000; the higher the score, the better it flushes. You can find the MaP score for virtually every toilet made online at

MMWD Rebates Get Paid to SaveIf you have old-style commodes installed in 2001 or earlier, and are ready to conserve more water and improve flushing performance, MMWD will rebate up to $150 of your purchase of up to two WaterSense-labeled toilets! To find out more about the rebate program visit



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