Backflow Prevention

So what is backflow? – & why should I care?

According to the World Health Organization, diarrheal disease accounts for an estimated 4.1% of the total DAILY global burden of disease and is responsible for the deaths of 1.8 million people every year. It was estimated that 88% of that burden is attributable to unsafe water supply, sanitation and hygiene, and is mostly concentrated in children in developing countries.

Imagine if one of your children were to become seriously ill, or even die – just because of drinking contaminated water!

This is in fact a daily occurrence in many countries that don’t have sanitary regulations governing the possibility for: contamination of the public drinking water supply. A common cause of such contamination is backflow.

Illustration courtesy of: The Morten Bay Regional Council.

Simply put; backflow is what can occur if there was a loss of water supply to your house (perhaps caused by a burst water main) and for example; a hose was left in a swimming pool while filling it. If the tap being used was not fitted with a vacuum breaker device, this could result in swimming pool water being sucked back up the hose into the main supply line: causing contamination of the public water supply (with swimming pool water).


With Hand held Bidets a similar scenario is possible: If someone had a blocked toilet (fecal matter in the bowl) and decided to use the hose of a Hand held Bidet (with the head unscrewed) to try to clear the blockage. The hand held bidet also did not have a non-return check valve, or if it did – the check valve failed. The only difference is that this time instead of chlorinated swimming pool water, we now have the possibility of introducing dangerous pathogens into the public water supply, which, if ingested in sufficient quantities have the potential to cause serious illness or even death.


Of course 6 individual factors must be present (and all at the same time), for it to be possible that a dangerous backflow incident with a Hand held Bidet could occur:

  1. There must be fecal matter in the toilet bowl.
  2. The wash gun must be removed from the hose (or the operating lever stuck open).
  3. The wash gun (or hose) must be placed below waterline in the toilet bowl.
  4. The isolating tap must be left on.
  5. The check valve must either be missing or fail.
  6. There occurs a loss of water pressure, or water supply to the premises.

The statistical probability of all six factors being present at the same time is obviously pretty small. Nevertheless, because it is technically possible for backflow to occur, combined with the fact that fecal pathogens have the ability to cause death if ingested in sufficient quantities, means that Hand held Bidets have been placed in the “High Hazard” category for risk of backflow by Australian Standards.

Some people mistakenly believe that the problem here is posed by possible fecal contamination of the bidet nozzle itself. Not so: if you think about it carefully; this would then apply equally to traditional bidets (Bidettes) which have an outlet above the rim of the pan. It is just as conceivable that the outlet on these bidets could become contaminated with fecal matter or bacteria caused by splash back, as the nozzle of a hand held bidet. By the way – for those who don’t know – hand held bidets are meant to be operated at all times from above the toilet seat (never from underneath) and when used like this are no more prone to splash-back than a traditional bidet.

But what do the Standards say about traditional bidets? Quote: “where the douche outlet is, in all positions, at least 25mm above the rim of the pan, NO backflow prevention is required”. The issue here is about backflow of contaminated liquid, not bacteria migration! For it to be possible that backflow of contaminated liquid occurs, the outlet of the bidet must first be submerged in a liquid. If the outlet of the hand-held bidet (in the lowest position possible) could never be lower than 25mm above the rim of the toilet pan, no backflow prevention would be required. This would of course make a hand held bidet very difficult to use, and so therein lies the problem. This by the way; applies equally to flexible shower outlets that could be left lying in a bathtub full of water, or (heaven forbid) even in a toilet bowl. The following note from the Standards indicates (to some extent) how they are formulated to be as “idiot-proof” as possible.

AS/NZS 3500.1.2003, NOTES:

“1. In assessing a potential backflow condition, consideration should be given to – – the probability of piping change, and negligent or incorrect use of equipment.”

So although Hand held bidets are included in the “High Hazard” category; there is actually nil risk of dangerous backflow occurring unless the hand-held bidet were accidentally/intentionally placed below water level in the toilet bowl itself – and why would any intelligent person do that?


.Under seat Bidets do present a less significant risk of dangerous backflow occurring; depending obviously on the distance the outlet is below the rim of the pan. In the case of the underseat bidet pictured left; this is a fair way down.

In this case the toilet must actually become blocked to the point of the water level covering the bidet outlet, for it to be possible for backflow to occur, i.e.:


  1. There is fecal matter in the toilet bowl.
  2. The toilet becomes blocked
  3. The water level rises to cover the bidet outlet
  4. The operating tap is left on.
  5. The check valve is either missing or fails.
  6. There occurs a loss of water pressure, or water supply to the premises.

In the absence of any direct reference in the Standards to this type of bidet, it must also be assumed that they fall into the “High Hazard” category for risk of backflow. This is simply because the outlet of every underseat bidet (in the lowest position possible) is always  less than 25mm above the rim of the pan.


A Traditional Bidette (photo left) presents no risk of backflow occurring because the outlet is at least 25mm above the rim of the pan. Water level could only rise to the point of flowing over the rim and onto the floor. (The outlet of the bidet could never become submerged unless the whole house became flooded)

Non-electric Bidet seats with a vacuum breaker device standing more than 25mm above the rim of the pan also fit into this category. So also do Above-seat Bidets; if the outlet is more than this regulation distance above the rin of the pan.



.Electronic Bidet seats depending on the design; either have their own separate little tank of water, or heat the water continuously as it is used. In both instances the flow of water is usually controlled by solenoids (electrically operated valves) just like your dishwasher and washing machine. This provides positive backflow prevention because if the solenoid becomes defective or suffers a power failure, the valve remains firmly shut. Electronic Bidets (Bidet Douche Seats) have  been given approval in the Standards to use a (non testable) approved dual check valve to meet backflow protection requirements. (See PDF below)


.Traditional Bidets

These bidets have an ascending spray (as in the photo left) and are classed in the “High Hazard” category for risk of backflow by the Australian & New Zealand Standards. Commonly found in European countries; these bidets undoubtedly do offer convenience superior to bidettes (conventional bidets with just a mixer outlet above the rim).

Nevertheless; connecting one of these appliances directly to a public water supply without the mandatory backflow protection devices (RPZ valve or RBT) would potentially be very dangerous indeed.



Check out the following extracts from the Standards for yourself if you are not convinced:

Backflow Prevention-Australian & New Zealand Standards


What do these regulations mean to the potential buyer of a Bidet?

Not a thing – if you are connecting the bidet to a completely independent water supply such as tanks or bore water, and there is no cross-connection with the public water supply.

However, if you are connecting the bidet to council water supply within Australia or New Zealand, you may want to consider any possible implications for not complying with the regulations. (Plumbers should comply with all the applicable standards, and all new buildings must pass a final building inspection).
By the way; if you study the above legislation carefully, you will concede that simply adding a non-return dual check valve to the installation does not constitute compliance with legislation. These in-expensive items are approved backflow protection for “Low Hazard” applications only, and this does not include: bidets with an outlet that can be in any position less than 25mm above the rim of the toilet pan (approved electronic models excepted). These appliances have been placed in the “High Hazard” category for risk of backflow by Australian & New Zealand Standards.

So let’s start off by clarifying the option of supplying correct backflow protection for these first 2 types of integrated bidets; (hand held and under seat models) with the most practical approved device:

A reduced pressure zone valve.

 Initial cost: $300
Installation: $200

Yearly test: $100
Total cost (over 2 years): $600

Add to this $150 – $300 for a good under seat or hand held bidet kit; and you have the entry price for a quality brand electronic bidet seat that is already compliant with regulations. (That’s assuming you already have a suitable power outlet available for your electronic bidet). If you are connecting 2 or more toilets to the same line, the option of providing compliant backflow protection with an RPZ valve starts to become more economical (2 toilets can now be equipped with hand held bidets for the same price as 1 Electronic Bidet Seat).

Some plumbers who are not aware of these regulations (or who don’t care); will install hand-held bidets without this valve. They do however risk being sued, if somebody were to then use the product they have installed incorrectly; and in doing so caused a dangerous backflow  incident to occur. Most plumbers will simply not want to take that risk – however small that risk may be.

Now you can understand why most people who want the convenience and low cost of a hand held or under seat bidet facility; (a) make sure it at least has a check valve, (b) hook it up themselves, (c) are responsible in its use, and (d) take it with them should they move or sell the house.


  • If you are installing a hand held bidet spray yourself; make sure the installation includes an isolating tap with non-return check-valve as a bare minimum. If the bidet (or hose) is subsequently never placed below waterline in the toilet pan – there is absolutely no risk of dangerous backflow ever occurring. Remember you will also need to install a PLV where water pressure is over 350kPa.
  • If you are contracting a plumber to install a hand held bidet spray:

Because these appliances are not yet common use in Australia; many plumbers, architects and building companies are quite ignorant of the regulations that apply to installation of hand held bidets (in Aust & NZ) – to a public water supply. Regardless; licenced plumbers are required to comply with Australian Standards, and any new building will not pass final inspection – if the mandatory backflow prevention devices have not been included in the installation.

    1. One economical way around this dilemma for licenced plumbers (who need to stay safe): install the T piece with isolating tap only (or a completely separate supply line with a tap), and then let the customer themselves install the bidet of their choice. This minimal plumbing work will comply with Australian regulations for connection of other types of bidet, such as an electronic toilet seat bidet.
    2. Alternatively; on new buildings with multiple toilets, it may be viable to supply all the toilets with water from the same supply line. This supply line can then be fitted with just 1 RPZ device and 1 PLV, but cannot be used to supply water to any other points (such as a wash basin).
    3. Where building renovation work is being done to existing (public) toilet facilities; the only legal option may be to install a separate RPZ device for each individual toilet. Remember this must also be installed in an accessible position, to allow for periodic testing – as required by local authority regulations.
    Are there any affordable, toilet-integrated bidet solutions that do comply with regulations – without these expensive RPZ devices?

    Happily – Yes!

    LuSan Bidets is pleased to be able to offer durable and economical alternatives to expensive electronic bidets; that do not require any additional backflow protection when used with the public water supply throughout Australia & New Zealand. One of the best known names in electronic bidets, Japanese manufacturer Toto have designed the “Eco Washer” to be an effective but cheaper alternative to their more expensive line of Electronic Bidet Seats.

    Another well known Japanese company Aisin-Seiki, have designed an excellent electronic bidet seat that is much simpler (and cheaper) than most other reputable brand electronic bidet seats. Unlike many comparable products; these non-electric & electronic bidet seat models have been designed with an in-built vacuum breaker device (just like a modern garden tap outlet) making it virtually impossible for backflow ever to occur.