Fresh Water Head Conversion & Contamination

I've read some of the prior threads on this topic... and am interested in doing this myself.

Coming from the RV world, every single toilet on the road is connected, in a lot of cases without even a backflow preventer, to the pressurized fresh water system... and of the 10 million or so RV owners in the US.. no one seems to be getting sick.

So, I must be missing something - please without pontification or doomsday advice... can someone point to cases of contamination actually happening and if so, root cause?

Cant document the contamination statistics but my last 5th wheel toilet and my current RV toilet on the boat both have the integrated backflow preventers (siphon breakers) you discuss that are factory installed.


Easy enough and cheap enough to install one.

Backflow prevented isn't a siphon break, it's just a one way valve. You'd need both. Toilets that are designed to be connected to the potable water supply require pressurized water and have the siphon break built in. The backflow preventer is typically a solenoid valve in the flush water inlet line, although some toilets including VacuFlush have a "water valve" at the back of the bowl.

Peggie, hi - have your kindle book, thanks for chiming in -

backflow valve is your belt and the siphon break is "suspenders" for when no freshwater pressure? (pump is off)

Again, have not seen this level of redundancy on land. I mean.. think about a residential toilet. Really neither of those devices are in play. Its just gravity, aka pressure.

Fresh Water Head Conversion & Contamination

Correction kev_rm: Every residential and commercial toilet has a vacuum breaker or air gap incorporated into it.

think about a residential toilet. Really neither of those devices are in play. Its just gravity, aka pressure.

The difference is, on land flush water is delivered to a tank above the bowl, so the fresh water plumbing never comes in contact with the bowl. The flush water line in a marine or RV toilet is connected directly to the bowl. Without the necessary vacuum breaker and backflow preventer, e-coli and other bacteria in the bowl can migrate into the fresh water supply.

Correction kev_rm: Every residential and commercial toilet has a vacuum breaker incorporated into it.

Nope...residential toilets that have a tank don't, and commercial toilets to which flush water is fed directly to the bowl don't either because the water supply is always pressurized...which essentially creates a backflow preventer. But on a boat or RV, the fresh water system is pressurized only while the water pump remains on.

I don't see a vacuum breaker in your drawing of a commercial toilet...and your drawing of a residential toilet is only the tank....and the flush valve is a flapper valve that's lifted when the toilet is flushed. So even if the tank overflows, there's no the water pipe that feeds the tank can feed the bowl directly.

I have 3 toilets in my house, all of different ages (house is 30 years old), all with different flushing mechanisms in the tank...the only flush valve in any of 'em is a rubber flapper valve in the bottom of the tank. On all of 'em a chain or a rod on an arm that the flush lever raises lifts it. And the ball cock only prevents the tank from overflowing by shutting off the flow of water when the correct level in the tank is reached. If it overflows, the floor gets wet...there's no way that water in the toilet bowl can ever get into the water plumbing.

The residential (or commercial) water supply is not always pressurized. The pressure can fail because of equipment failure, broken pipes or even intentional shutdowns for maintenance. This is why appliances including toilets have built in cross contamination features and why backflow preventers are recommended and sometimes required for outside faucets and irrigation systems.


Anyone who would ignore the possibility of cross contamination on his or her boat is a fool and a soon to be very sick fool. Install nothing that isn't designed from the factory for pressurized fresh water if fresh water flushing is what you want.

WesK said:

The residential (or commercial) water supply is not always pressurized. The pressure can fail because of equipment failure, broken pipes or even intentional shutdowns for maintenance. This is why appliances including toilets have built in cross contamination features and why backflow preventers are recommended and sometimes required for outside faucets and irrigation systems.


Anyone who would ignore the possibility of cross contamination on his or her boat is a fool and a soon to be very sick fool. Install nothing that isn't designed from the factory for pressurized fresh water if fresh water flushing is what you want.

Click to expand...

If you're going to call people names, give me ONE EXAMPLE of someone getting sick and their system design that contributed to it.

HeadMistress said:

think about a residential toilet. Really neither of those devices are in play. Its just gravity, aka pressure.

The difference is, on land flush water is delivered to a tank above the bowl, so the fresh water plumbing never comes in contact with the bowl. The flush water line in a marine or RV toilet is connected directly to the bowl. Without the necessary vacuum breaker and backflow preventer, e-coli and other bacteria in the bowl can migrate into the fresh water supply.

Click to expand...

I don't know, this is pedantic but there is a path... its just uphill. it doesn't get dry in between flushes..

Anyone with basic skills can redesign head systems...as long as a few basic principles are applied.


Some people are skeptical that others have brains.


But it is important to understand the basics and hw to prevent cross contamination of water sources.


To me it is the most basic of all systems on a boat.

I winter in the water. Contamination issue addressed and aside; Any reason not any to add valves so that during the winter I draw salt water instead of fresh?

cyfarkas said:

I winter in the water. Contamination issue addressed and aside; Any reason not any to add valves so that during the winter I draw salt water instead of fresh?

Click to expand...

It's not that easy. Toilets designed to use pressurized flush water don't have intake pumps, so you'd have to install a remote intake pump and plumb it to replace the fresh water line. Teeing into it risks contaminating your potable water supply with sea water.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
http://www.amazon.com/New-Get-Rid-Boat-Odors/dp/1892399784/

This is more easily done with a manual flush head. With an elactris flush head you will probably need to have a saltwater pump pressure system. If you have an anchor wash down pump, that system is operating ar 70psi. That is more than you would want in this case a separate 40psi pump could be used to supply the system. As long as you are sure that you won't get salt water into the fresh ware system. That might be harder to achieve than you think.

Thank you tadhana. The anchor wash down was my target. The pressure info helps.

It would be pretty easy if you already have a saltwater wash down system.

I have a wash down system. so I added a small 12V solenoid valve plumbed to the wash down system and wired in with the flush switch.

Instead of teeing into the flush, can you just disconnect the fresh and connect the salt so there's no chance of cross contamination?

As long as the water pressure is maintained on one side of the solenoid valve, doubt the extra pressure would affect the head. It should be free lowing at that point as long as the hose goes straight to the bowl flush rather than some internal valve.


That is where it might get tricky depending on which head you have.