1: Toilets
Summary
It is essential that toilets flush effectively to maintain standards of hygiene, but designs are now available that use significantly less water than was required in the past. In older properties, flushing the toilet represents the largest proportion of water used in the home. An average household with a nine litre toilet flushes around 110 litres down the pan – that’s 30 per cent its total water consumption per day. This should reduce as older toilets are replaced with newer ones with lower flush volumes. Toilets in offices, schools and public conveniences account for an even greater proportion of total water use although the exact percentage will depend on factors such as whether urinals are available.
Valves and siphons
Before January 2001, all domestic toilets in the UK had to use a siphon flush, which was originally developed to prevent water wastage. When we pull the handle, a piston lifts water to start a siphon, which empties the cistern into the toilet bowl. When the cistern is empty the siphon is broken and the cistern refills ready for the next flush.
Since January 2001 approved drop valves and .flap valves have been permitted. These allow a button operated flush and more obvious two-button dual-flush operation. But sooner or later, unlike the siphon, they will leak. The Water Regulations require endurance testing of 200,000 flushes under laboratory conditions, but mechanisms can be incorrectly installed and debris can enter the cistern during installation, causing immediate leaks. Evidence from water companies shows that leakage from valves is already becoming a serious problem.
From a sample of over 500 properties that were investigated due to unusually high water bills, Bournemouth and West Hampshire Water identified 31 properties where the cause of the high water use was leaking drop valve operated toilets. On average, six month water bills for these properties were over £370 more than the bill for the six month period before the leak.
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Detecting a leaking flush valve |
Dual flush
Dual flush siphon and valve flush toilets both offer potential savings, particularly in the home. For commercial and public toilets, the savings are likely to be less, as users may not know how to use the system and will often have no financial incentive to save water.
Typically the effective flush volume has been calculated as the average of one full flush and three reduced flushes. Therefore a 6/4 dual flush toilet should average 4.5 litres per flush, but this figure can vary depending on who is using it.
Low-cost retrofit options
One of the most cost effective domestic water efficiency measures is to convert an existing toilet to variable flush and/or to optimise the full flush volume. Retaining the original siphon avoids the problem of leaking valves.
Effective flushing volumes
An effective flush volume is the volume of water needed to clear the toilet pan and transport solids far enough to avoid blocking the drain. In reality, few toilets when fitted flush with the optimum volume of water. Too little water will lead to double flushing and increased risk of the drain blocking, whilst too much will waste water. Many devices are available to avoid wasting water. Some displace a volume of water in the cistern and so reduce each flush by an equivalent amount, typically one litre. Before and after you fir this type of device check that the flush works well, that the inlet valve does not leak and that it is adjusted so that the water is up to the level marked in the cistern. Lowering the water level will reduce the flush volume, but may also make the flush less efficient. Cistern displacement devices are often available free of charge from local water companies, or a suitable plastic bottle filled with water can be placed in the cistern.
If double flushing is needed to clear the pan, the amount of water used could actually increase. If there are problems with flushing, remove the cistern displacement device immediately.
Variable flush devices
These devices allow the user to choose how much water is used for each flush. Some allow a flush to be interrupted once the pan is clear and some allow one of several pre-determined flush volumes to be selected before flushing. Fitting variable flush retrofit devices resulted in an 8.5 per cent reduction in total domestic water use in trials by water companies and the Environment Agency.
Individual households have achieved even greater savings with no evidence of double flushing. Many older toilets are already fitted with dual flush siphons, but with the dual flush function disabled by adding a small plug. Removing this plug converts a nine litre toilet into a 9/4 dual flush and requires the flush lever to be held down to achieve a full flush.
Retrofit devices that follow the same ‘pull and hold for full flush’ are available. This seems logical but people will need to be told what to do. Whilst instruction stickers are supplied, these are often not fitted for aesthetic reasons.
The Thomas Dudley Duo siphon is designed so that it defaults to full flush. Whilst there is a risk that users may never discover the part flush function, visitors will be spared embarrassment and repeated flushing.
Delayed action inlet valves
As a toilet flushes, it immediately starts to refill so the actual flush can be significantly greater than expected. In a simple test, Portsmouth Water researchers found that a 5.8 litre flush increased to 6.8 litres with the inlet valve left on during the flush – a 17 per cent increase. This problem is solved by the Torbec Ecofill inlet valve which stays shut until the flush has stopped.
Do low flush toilets cause drain blockage?
Properly designed and correctly installed toilets with flush volumes as low as four litres can be connected to conventional drains without fear that the drains will become blocked6. When the existing nine litre toilets at St Leonard’s Middle School, Hastings were replaced with four litre water efficient models, the previous problems of bad smells and blockages disappeared. For flush volumes lower than four litres care may be needed with the design of the drain.
As the amount of water we use has increased considerably since most of the UK’s sewers were built, sewers (mains drains) are no more likely to become blocked due to less water being used to flush the toilet or indeed due to any other water efficiency measures.
Regulations
Toilets that are to be connected to the mains water supply must meet the Government’s performance specification. Water Regulations Advisory Scheme (WRAS) approval is the best way to demonstrate that a product complies, but there is no legal requirement to independently test and verify products.
For more information about toilets read the full chapter using the link below.
This information gives guidance only. It should not be treated as a complete and authoritative statement of measures to be adopted and their results. You are advised to make your own investigations before deciding on any course of action. The Environment Agency does not endorse the use, purchase and/or the performance of the goods or services provided by companies mentioned herein.
