Watertank Mains Water Switching Devices; Are They Necessary?

One of the greatest disincentives to harvesting rainwater is the often misinterpreted legislated need to fit an automatic mains water switching device when the pump supplies water for sanitary flushing. These devices switch from tank water to mains water when the tank runs low but a plumber's or builder's lack of regulatory knowledge not only imposes an unnecessary financial impost to buy an automatic mains water switching device, it also imposes an additional plumbing cost. It is also something else that can go wrong.

People need to be aware that automatic devices do not *always have to be fitted. As an example, I will show the legislation applicable to Victoria.

*Currently, South Australia and some areas of QLD have overridden the Plumbing Code of Australia and do not allow manual devices. This is a very poor regulatory decision, nevertheless, homeowners need to check their area's applicable regulations.

I have linked the Victorian Building Authority Technical Solution Sheet 5.08 below that deals with rainwater supply to cisterns..

http://www.vba.vic.gov.au/__data/assets ... sterns.pdf

The advice given in 5.08 is the same as that given below...

STATUTORY RULES 2008
S.R. No. 136/2008
Building Act 1993
Plumbing Regulations 2008
The Governor in Council makes the following Regulations:
Dated: 18 November 2008
Responsible Minister:
JUSTIN MADDEN
Minister for Planning
RYAN HEATH
Clerk of the Executive Council

PART 7—REQUIREMENTS FOR WATER SUPPLY WORK
10 Definitions
In this Part—
automatic or manual interchange device means a device that by way of manual or automatic means can alternate between varying water sources;

Requirements where rainwater used for sanitary flushing.
(1) If a reticulated water supply from a network utility operator is connected, or proposed to be connected to a building where a rainwater tank is installed for the purpose of sanitary flushing, an automatic or manual interchange device that allows alternate use of water from the rainwater tank or the reticulated water supply must be installed to ensure that there is a continual supply of water for sanitary flushing.

Figure 1 in Technical Solution Sheet 5.08 shows two methods by which a cistern can be plumbed to a water tank pump. The right hand side cistern is fitted with two cistern valves, one connected to the mains water and the other connected to the supply from the water tank pump. In the second instance, there is no need to purchase and plumb an automatic mains water switching device as the installation complies as a manual switching device. Savings can be several hundred dollars.

http://www.vba.vic.gov.au/__data/assets ... sterns.pdf

The above installation is compliant as per AS/NZS 3500 Part 1 Water Services, Section 14.

Many cheaper bullet proof manual switching devices are available that comply with the regulations. The MainRain linked below is popular.

http://www.mainrain.com.au/mainrain-features.html

If your builder or plumber is telling you that you MUST have an automatic mains water switching device fitted, don't fall for their spiel. There are alternatives provided a local regulatory body has not foolishly overridden the Plumbing Code of Australia.

Every year, the public spends millions of dollars unnecessarily on automatic devices.

EDITS: Updated obsolete PIC link to new VBA link, linked the MainRain link, warning about some areas overriding the Plumbing Code of Australia, other tidy ups.

A good point.................. but as most new houses have at least 2 toilets isn't it better to go the dual check valve installation and run a single pipe to each toilet than run 2 pipes to each?

Hi SaveH20

Thanks for posting up the info, You may have posted this in response to our previous discussion where I mentioned I was advised by my plumber/building surveyor it had to be automated (at the tank end)

Had I known this piece of info I would have plumbed my pipes like you suggested (2nd option)

Unfortunately my plasterboards have just been installed 1 week ago, so it's not viable to do so.

I hope this valuable information helps someone else.

I will show this to my plumber and hopefully he will advise future customers accordingly.

It's not just the money saved, but you're also not relying on a machine to switch to mains water. And we know machines never break down! lol

Actually I thought about Bashworth's comments, can I run a single valve near the water tank to service 3 toilets?

That way I can still use a simple water pump?

Hi Brian,

A good point as usual.

I agree that it would not be practical to consider the optional fitting for two story houses for example unless a separate line was plumbed to a low level 'high use' toilet so that the option of having gravity feed could be incorporated. Having the pump sited near the 'high use zone' would save on AUSPEX and fittings plus a two valve system is very quick and easy to install.

There are also tank top up devices available that slowly feed a limited amount of water into the tank to maintain an adequate supply to the pump and this option is much cheaper to buy and plumb than having a mains switching device. It does however means that the pump will be using energy to deliver mains water that is delivered to the property under pressure.

The issue is that people are being told that they have to use an automatic switching device and are given no other option. The available information stream is inhibited by the existing situation whereby plumbers have no training in rainwater harvesting or require qualification to do the work. Most installations I see are sub standard and often non compliant. This manifests in poor yield, pipe blockages, stagnation, early pump failure, tanks overtopping in heavy rain, poorly optioned tanks, small roof areas harvested and additional costs to the home owner.

Hi JB1,

The plumbing situation between a new house under construction and an established home is often different. I see a lot of non compliance with new homes but I am only ever called out to provide answers after the fact.

A recent example with an established house was familiar where the client had a quote to harvest from one downpipe (Melbourne) to a 5,000 litre slimline tank. The quote included $1,000 for a pump and mains switching device (that he was told he had to have) to supply one toilet but the owner also wanted a connection to the laundry but this wasn't included in the quote.

A quick inspection established that...

The downpipe only serviced 30 sq m of roof. This would have supplied toilet flushing for two persons and nothing else.

The slimline tank would have never filled. Slimline tanks are also virtually impossible to clean and they are expensive. This one was $1,550.

Rainwater will now be supplied from three downpipes supplying a 3 x 2,100 litre tank (6,300 litres) settling system servicing the toilet AND laundry.

Over $750 will be saved by not using the mains switching device and previously suggested pump.

Using the superior and greater volume three tank settling system saves about $500 on the cost of the previous slimline option.

Downpipes will not be diverted, only water. This is neater and also cheaper.

The tanks will not be fitted with overflows for further cost savings as the water will automatically flow down the downpipes when the tanks fill.

The new installation will be much cheaper and the installation is also elegible for a $1,500 Victorian Govt rebate.

Another switching device bites the dust!

Save H20,

Hmm for my situation. New house, 3 toilets and single water pipe supply to each.

Is there any way I can get away with using a single one way separate valve near the tank so I can get away with a normal garden pump?

I'll also take your advice and use a round tank instead of slimline.

Thanks
John

Hi John,

I just read through your other replies on the other thread and see that you have an upstairs toilet. If your plumber was going to use a mains switching device, then the mains line would be plumbed to all three toilets as you say.

You have two other options.

1. Install a manual change over valve (interchange device) instead of the automatic mains switching device. This would require you to go outside to manually change over but most people with tanks are aware of how much water is in storage plus many also develop an awareness of dry spells and an interest in checking the BOM radar.

2. Install a tank top up device. These are simple and cheaper.

http://www.apexvalves.co.nz/plumbing/apex/rainaid.html
These are usually about $120 and do not require power.

There are others available that require a power point.

I have seen mains switching devices fail and there are threads on Whirlpool and other forums where people have had expensive problems. They also limit your choice of pumps.

Hi, the tank top up device looks interesting, but would either option allow me to pass the regulations (of which I know little about) for a new house.

I.e. can I achieve Certificate of Occupancy with the tank top up or manual change over?

I would prefer it to the more expensive and complicated pump with auto switch device.

You are in Victoria and the manual change over is ok as per the Plumbing Code of Australia (PCA) 2008 which state...

Requirements where rainwater used for sanitary flushing.
(1) If a reticulated water supply from a network utility operator is connected, or proposed to be connected to a building where a rainwater tank is installed for the purpose of sanitary flushing, an automatic or manual interchange device that allows alternate use of water from the rainwater tank or the reticulated water supply must be installed to ensure that there is a continual supply of water for sanitary flushing.

A top up device is classified as an automatic device and it supplies a limited amount of water (100 mm ) to the tank when the tank's water level reaches a critical low point. See earlier RainAid link.

A top up device does not isolate the pump like an automatic mains water switching device like a Rainbank or WaterSwitch does. Water is still pumped from the tank to the toilet.

A manual change over device like the MainRain is simply a valve that is manually opened or closed to alternate supply between mains water and rainwater. Manually switching from rainwater to mains water isolates the pump from the cistern(s).

Plumbing regulations require check valves to be fitted when rainwater is plumbed into a mains water pipe to prevent cross contamination with rainwater and mains water. Naturally, this applies to both manual and automatic switching devices.

While it is often cheaper and neater to install a top up device rather than an automatic switching device, it is still best to isolate the pump and switch to mains water during a long dry period rather than pump water that is delivered to the property under mains pressure.

When automatic switching devices fail, they can cost several hundred dollars (plus labour costs) to replace.

The Acquasaver is an automatic mains water switching device that is unpowered as it operates by hydraulic pressure. It is also tough and reliable. Note that it is not compliant for potable use.

http://www.acquasaver.com.au/

Plumbing a separate water pipe from the pump to separate toilet cistern valves qualifies as a manual mains water switching device as the mains water supply and rainwater supply to the cisterns both have small isolating valves fitted to the toilet walls. It is a very neat, trouble free and inexpensive way to supply the cisterns. The cistern valves also provide an air gap. See diagram in the link (also previously linked) below.

http://www.vba.vic.gov.au/__data/assets ... sterns.pdf

Plumbing a separate rainwater PEX pipe that branches off to all toilets is easy during the early building stage. If plumbing rainwater into a mains pipe, it must be remembered that rainwater is naturally acidic. As such, it can react with copper pipe.

Hi John/JB1,

I have received the following written advice from the Rain Aid's Australian distributor...

"The RainAid RA2L complies with the Victorian regulations for use as an automatic switching device and is used extensively throughout Victoria for this application".

Thanks Champ!

You saved me a few hundred dollars.

I'll get the Alko afterall.

I'll call up RainAid and see where I can get buy one.

The Rain Aid comes in two variations and there is plenty of information and diagrams online.

The G Store at 1095 Dandenong Rd., East Malvern might be close to you and they have them for $130. The website doesn't say if this is for either model and so I assume that you have a choice. The 2 litres per minute one seems to be the biggest seller but this probably comes back to Sydney Water regulations.

Perfect! The G Store was were I was going to buy my auto-switching pump anyway!

They were recommending an Italian made unit for ~$700 previously.

I assume that you will be using the water for something more than solely for sanitary flushing given that the 95 sq m roof area you intend harvesting (stated in another thread) will harvest approximately 55,000 litres per annum after roof evaporation losses etc. You generally allow about 8,300 litres per person per annum for sanitary flushing.

If you also plumb the pump to a dedicated rainwater garden tap, it is best to use a large diameter pipe to reduce friction loss. I have seen small diameter copper pipe that has been used by plumbers and cringe. Copper pipe should never be used anyway as rainwater is naturally acidic.

For garden watering, you are better off to buy an 18 mm garden hose and attach a short length (maybe 1.5 metres) of 12 mm garden hose to the end so that you can use the standard 12 mm hose fittings. You join the two hoses by using a poly 18-12 mm reducer and two s/s worm clamps. At 20 litres per minute, the 18 mm hose has 8 times less friction loss.

One of my clients was recently sold a pump for $1,200 by a plumber because my client wanted to water the garden as well as supply the cistern. All he needed was a $250 pump and an 18 mm hose!

For anyone who is reading this that is considering harvesting rainwater to supply a cistern only, you only need a small pump as cisterns fill slowly. As pumps operate with lower pressure than mains water but the cistern valve seal is designed for mains pressure, the flow path efficiency can be improved and life made easier for the pump if the seal is replaced with a low pressure seal. To do this, you...

Buy a Fluidmaster 400UK063 cistern valve (about $20).
Buy an optional very low pressure gravity fed seal 242LP071 (about $2.50 - $3.00).
Remove the 'pigs tail' flow restrictor from the bottom of the valve shaft (use needle nose pliars and pull out - it is plastic).
Remove the standard seal and replace with the 242LP071 seal. Be very careful to hold the float arm up when you twist the cap.
Fit the Fluidmaster to the cistern (you only do up one plastic nut).