Low Flow Toilets | Everything Explained

Did you get another ridiculously high water bill? Perhaps you cringe every time the kids run into the bathroom. All that water just going down the drain. Is there a way to lower your water usage and protect the world’s water supply? Many professionals will suggest low flow toilets. But is it the perfect solution to your water woes?

In this post, I’ll explain what a low flow toilet is, how it works as well as answer some popular questions on the topic.

Let’s dive in!

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What Is A Low Flow Toilet?

What Is A Low Flow Toilet?

A low-flow toilet is defined as a toilet that uses no more than six litres of water per flush, compared to 13 litres or more required to flush an old-fashioned loo. While low-flow toilets are not required per plumbing regulations, they are much easier to find these days compared to the older style due to an international trend towards water conservation. 

After the original introduction of low-flow technology in the 1990s, a dual-flush system became an even more attractive option. Dual-flush toilets feature a button or lever, so you can flush liquids using just three or four litres of water. Opt for the second setting and use the toilet’s entire capacity to wash down solids.

You can find these toilets in a huge variety of designs that can look just like an old-fashioned high cistern Victorian piece or a sleek modern unit with a hidden cistern. Basically, the big difference you may experience while using one is noticing less water sitting in the bowl between uses and sometimes a noisier flush.

Why did the plumbing industry make the change to low-flow? The average person takes a pee six or seven times a day. Multiply that number by 13 litres, and you have an excessive amount of water being used simply to move less than two litres of waste out of your house. And it all must be treated before re-entering the water supply.

Basically, toilets were a huge waste of water, energy, and money. The low-flow toilet looked like the answer to the first world demand for sanitary facilities in every home, hotel, and sometimes every bedroom.

Low Flow Toilet Cost

Finally, the cost to install a low-flow toilet is comparable to a traditional version. You will spend between £100 and £300 on the piece of sanitaryware and another £200 on labour.

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How Does A Low Flow Toilet Work?

There are a couple of versions of the low-flow toilet. The earliest designs used the old cistern/gravity approach. The six or seven litres of water are stored in the cistern. When you pull the lever, a flapper valve opens that lets all the water rush through, carrying any waste with it down your pipes. Obviously, the old 13 to 30 litres did a much better job of washing it all down compared to seven litres.

Since some gravity toilets struggled to clean the bowl after each use, pressure-assisted designs popped up. Air is used to push the water down the sides of the bowl, giving it more force than gravity alone. Some pressure-assist toilets simply use negative air pressure while others add an electric pump to ensure everything flushes as expected.

A couple of years ago, the earlier gravity low-flow designs were criticised as leaking worse than traditional toilets and defeating the entire water-saving approach. The experts found that 8% of the new toilets leaked, and wasted up to 400 litres per day! However, a few manufacturers such as Toto from Japan never used the old gravity design and do not suffer from the leaking problems.

Unfortunately, since we have viewed the toilet as a bulletproof technology for so many decades, many homeowners do not do any research when purchasing a toilet. We all figure it will work the same no matter how its exterior appears.

If you want to really save water and money, explore user and industry reviews before buying any low-flow toilet.

Advantages of Low flow Toilets

  • Saves up to 35% of your daily water usage per person, per day
  • Eco-friendly
  • Costs the same as the traditional toilet
  • Features both modern and vintage exterior designs
  • Can dramatically lower your measured water charge

Disadvantages of Low flow Toilets

  • Not all low-flow toilets are equal
  • Some designs do not remove all solid waste and can clog
  • Some designs leak as valves do not properly seal
  • Bad toilets can waste between 200 and 400 litres per day
  • Requires more research to find a well-performing unit

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Do low-flow toilets clog more easily?

It all depends on the low-flow toilet sitting in your water closet. Those 90s toilets did not change the size of the lower waste pipe, so they did clog more often as there was so much less water pushing the solids down the drain. Newer toilets have increased the size of the waste pipe to 75 mm instead of 50 mm, which results in fewer clogs.

Do low-flow toilets clog more easily?

How do you know if you have a low flow toilet?

Every toilet manufactured features an embossed stamp on the bowl near the back by the cistern. Look for something that says, “6 lpf/1.6 gpf.” If the lpf number is higher or the stamp is missing, it is likely not a low-flow toilet. 

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Can you make a regular toilet low flow?

While you can do a couple of tricks to lower water usage on an old-fashioned toilet, you cannot make it truly low flow. 

  • Drop a brick into the cistern, and you can save two litres per flush.
  • Bend the float rod so that the toilet shuts off its fill cycle earlier and save one litre per flush.
  • Check the shut-off valve for leaks.
  • Replace the flapper valve if the toilet is always filling.

These simple fixes will help with water conservation and also save you money on replacing a perfectly functional toilet with one that may not perform as expected.

Final Thoughts…

There you have it! Everything you need to know about low flow toilets.

While not all low flow toilets are created equally, finding and installing a good one can save you hundreds of litres of water a week (or even a day) as well as saving on your water bill and being kinder to the environment at large.

So, will you look to install a low flow toilet in your new bathroom?


Michael R

Michael is a KBB designer from the UK. He's been designing and project managing new Kitchen, Bedroom and Bathroom installations for over eight years now, and before that, he was an electrician and part of a KBB fitting team. He created The Bathroom Blueprint in early 2020.