Single Flush vs Dual Flush

There are lots of ways to categorize toilets. One is by basic external design – two-piece, one-piece, or wall mounted. Another is by flushing mechanism, pressure assist versus gravity feed. But a third might be the most important of all: single flush versus dual flush.

After all, the first is chiefly an issue of cleaning or convenience or even just appearance. The second is an internal design issue. But the last way of distinguishing them can be critical in determining how well the toilet actually works in your home.

That said, beyond the meaning implied by the names, what is there to being a single flush toilet rather than a dual flush model? As it turns out, quite a lot.

Some Definitions

The names “single flush” and “dual flush” can be a little misleading. They don’t actually refer to the number of flushes the toilet performs when you press. They refer to a mechanism on the toilet, one that lets you choose one over the other. It signals the release of a certain volume of water versus double that amount.

You might have seen those circular flushing buttons on the top of a toilet where the circle is divided into two “moons”. The mechanism is intended as a water-conservation technology. One button is used when you need to dispose of only liquid waste. You hold down both when there’s solid waste to flush. Some designs have a handle instead that you can pull up or down but they’re less common.

Now, while it might sound obvious, it’s a good time to ask: what is a “flush”?

In one way, it’s obvious. It’s the flow of water that removes the waste when you push the toilet’s handle or button. Interestingly, behind that simple truth there is both legal complexity and some practical consequences. Knowing a bit about both can help you choose the best toilet for your circumstances.

The Law

First, the law. In the average home, toilet use is responsible for about 30% of total residential water use. Today, more than 4.8 billion gallons of water is used to flush waste down toilets, or an average of 9,000 gallons per year per home. That’s a lot of water. So, the Federal government got involved to enforce conservation.

The Department of Energy, as a consequence of the Energy Policy Act of 1992, established a regulation that toilets made after that could use no more than 1.6 gallons per flush (GPF). It took effect in January, 1994. The EPA also got involved and, in 2006, established their WaterSense program. Businesses can earn that label on certain products by following certain guidelines. One of them is to use no more than 1.28 gallons per flush.

Most toilets today are low-flush toilets that use no more than 1.6 GPF. There are some exceptions, mostly revolving around the needs of the handicapped, but almost all toilets follow that rule today. In some states the restrictions are even tighter; California law requires that toilets sold there use no more than 1.28 GPF.

The Consequences

That’s the legal situation. The practical consequences are pretty obvious. All over the country there are legal restrictions on water use that affect toilet designs. As one reaction, manufacturers responded by designing single-flush toilets, dual-flush models, High Efficiency Toilets (HET), and more. Some WaterSense models combine high efficiency with dual-flush technology.

Of course, there is government-enforced ‘efficiency’ for the sake of following a rule or earning a label and then there is efficiency in the real world. Not all low-flow toilets actually do the job intended: getting rid of waste cleanly. That’s why it’s essential to do more than just look for a WaterSense or HET label. It’s important to actually read some reviews to find out who is just following rules and which models actually perform well.

That’s particularly true because, as these things usually go, there are exceptions. In some cases, those exist to satisfy the needs of individuals with special health circumstances. In other situations, it’s the manufacturer’s response to differing state-level regulations. With the ability to order over the Internet and have a unit shipped from one state to another, things can get tricky.

In still other cases, it’s “grandfathering”. That is, the law doesn’t require replacing older toilets to meet the standard and toilets can last a very long time. If you have a home older than about 20 years old you likely have one. But if you plan to replace one you’ll be faced with the new standard.

Efficiency, Detailed

A single-flush toilet is the type you will invariably find in an older home (unless it’s been replaced). They may use as much as 5 gallons per flush if they’re really old or particularly inefficient.

One way to increase the efficiency is to “artificially” decrease the amount of water the toilet uses. A typical method is to simply place something inside the cistern or tank that takes up space. That forces the water level up higher while actually using less water.

That method is crude but effective, provided you use something that doesn’t decay like a well-sealed plastic gallon jug. And, most importantly, provided it still does the job of getting rid of waste with one flush. Efficiency means nothing without effectiveness.

Another way is to implement something called a “cistern converter”. That’s a kit that replaces your old-fashioned flush handle with the newer dual-button mechanism found on dual-flush toilets and controls water level.

Another method of increasing efficiency is, of course, to buy a newer toilet such as a dual-flush model or an HET. Using one button can result in using as little as three liters (0.8 gallons) of water; the dual-flush option typically uses six liters (roughly 1.6 gallons per flush). Some HETs can actually perform as well or better using even less water.

The net result of using one can save you around 6,600 gallons per year, on average. Given what utility companies charge today that can add up to a very substantial savings on your annual water bill.

Single Flush vs Dual Flush – Pros and Cons

Of course, that amount of potential water savings (and therefore cost reduction) can make installing a dual-flush toilet seem like a slam dunk decision. It might appear that, for a modest upfront investment, you could lower your water bill enough in a year or two to more than pay for the toilet.

Naturally, whether that turns out to be true depends on a lot of circumstances: the initial cost of the toilet (plus any installation charges), the amount of water you and your family use in a year, your utility rates, and so forth.

But, beyond the issue of cost (and the hassle of replacing a toilet), are there other things to consider when – pardon the pun – making the plunge to buy one versus the other? It won’t surprise you to learn that there are.

User Friendliness

One of the first considerations when deciding between a single-flush model and a dual-flush unit, even when the first type is a new high efficiency model, is what I call “user friendliness”. The term comes from the computer software industry but it applies here as well. You want the thing to be simple and easy to use without requiring any thought.

If you’ve ever used a dual-flush toilet you might know what I mean already. Sometimes, it just takes a lot of force to push the buttons. For many users, that’s not much of an issue. They’re not that hard, after all. But for the elderly, or those with arthritis and others with physical limitations, it can be. That’s one reason the law makes exceptions for such individuals.

There’s also the fact that the two buttons are generally placed in one circle and you have to press one finger or two down into a shallow hole to operate the toilet. Most of us can push one without pushing the other. The visually impaired or those with some motor control difficulties might not find it so easy.

Those difficulties can be amplified by simple confusion. It can be hard to remember which button is for the half-volume flush and which for the full flow. As a result, it’s possible to use the wrong one. Using the full flow for flushing liquid waste defeats the purpose by wasting water. Using the half-volume button accidentally does, too, and even more because you then have to press both for full volume on a second try to flush solid waste.

You don’t have to be suffering from a medical mental condition to make that mistake. I flatter myself I’m still reasonably aware but I’ve done it more than once. Some manufacturers get around that by clearly labeling the buttons (or even making them different colors or size), but the practice is not universal.


One other, likely greater, concern with a dual-flush model is whether it actually performs well. A dual-flush model typically holds less water in the toilet bowl than a traditional single-flush design. Here, I’m talking about the two basic designs, not a traditional model that’s been converted.

That can be a simple esthetic issue. Some people just associate more water in the bowl with better looks. But it can also be a functional matter. Streaking is more likely when there is less water initially in the bowl. It’s just a lot harder to remove solid waste from the sides after the fact, no matter how well glazed the bowl is.

Multiple flushing to counteract that essentially defeats the purpose of water conservation, a notorious drawback of some poorly designed low-flow toilets. Not to mention, that’s just plain annoying. Few of us want to stand above the toilet for a minute waiting to initiate a second (or third) flush.

The issue can go beyond the cost of water or inconvenience, though. It can be a health hazard. Waste left in the bowl is, clearly, a host for germs and practically no one is going to want to scrub the bowl after every bowel movement. Even beyond removing streaking, more water generally means a more thorough cleansing of anything inside the bowl. It also helps in getting rid of material well up the sides or even under the rim.

Many HET designs compensate for low water use by high pressure, improved materials, more intelligent geometry, bigger traps (the hole where the waste goes), and other methods. Some single-flush and dual-flush models both employ those tricks of the trade.


So, for all these reasons, it’s important to do a little study, read some reviews, and choose carefully if you plan to buy a replacement toilet. The choice between single flush and dual flush isn’t always simple. But, since they are sometimes pricey and because you plan to keep and use your toilet for years, it’s worth a little extra effort upfront.

It’s not the kind of topic most people will take joy in studying. But if you’re remodeling or just replacing an older unit, or maybe building a new home from scratch, it can potentially save you a lot of money and grief to get a little education on single-flush versus dual-flush toilets.

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