Where can white PVC be used for potable water?

[harrymusgrave]

My well is about 100 feet from my house. White PVC (underground) carries water to the pressure tank, which is under the house (house is post and pier construction on top of solid rock). I had all the rough plumbing done by an old hand from Oahu. Now I have to finish myself or fly him back and I really don't want to pay airfare and room/board and $50/hr. He did a really nice job of copper plumbing and the ABS waste is pretty nice too, but I think I can hook up all the fixtures myself. Money is an issue these days, or I wouldn't DIY it.

I have to connect the water to the house cold line, going through filters and UV. Can white PVC be used for any of this? I was thinking of using white PVC up to one side of the UV, and copper on the other side.

There is a reason I'm avoiding CPVC, so I really need to know if the white PVC is acceptable. It is all under the house with no direct light.

[Terry]

An interesting question.

Plumbing code allows PVC outside the foundation.
Can't be used for hot.

If it were being inspected, that would be a question for the local inspector.

You could try it that way, it would work, but would also likely get turned down on inspection, but then only your local inspector would know.

[jimbo]

Why are you avoiding CPVC??

As to the PVC, it is totally acceptable for potable water. The problem is that its rated maximum working pressure drops off markedly above 70ºF, and that is why it is not allowed to be used inside the dwelling. For what you are proposing, which seems to be cold water only, I don't see any real problems.

[Terry]

Jimbo,
I didn't know that.
Now it makes perfect sense why you wouldn't have it above ground.

By the way, the weather forcast for Hawaii for the next few days is 79-81
Kind of cool, most of the time it's closer to 88.

The problem is that its rated maximum working pressure drops off markedly above 70ºF, and that is why it is not allowed to be used inside the dwelling.

[jimbo]

For those who would like to curl up with a some nice zippy reading on a Sunday afternoon, try the 222 page PVC piping manual, at ppfahome.org. The manual is for commercial and industrial piping, but gives us an idea of the issues dealt with by those who write residential plumbing codes:



This is from PPFA:

Table 7. Temperature Correction Factors for PVC Piping

Operating Temperature (°F) Correction Factor
70 1.00
80 .88
90 .75
100 .62
110 .50
120 .40
130 .30
140 .22

140+ Not Recommended


In addition to the above, there are issues of designing the piping installation to accomodate the thermal expansion characteristics of plastic pipe, which is much greater than metal pipe.

Thermal Expansion and Contraction

PVC compared to non-plastic piping has relatively higher coefficients of thermal expansion.
For this reason, it is even more important to consider thermal elongation and contraction
when designing PVC piping systems.
Table 9 lists the amount of movement of PVC piping per length of run. However to
calculate the exact expansion/contraction of PVC piping, use the Constant factor of Y =
0.36 and the following formula:
Example: How much expansion will result in 300 ft of PVC pipe installed at 50°F and
operating at 125°F?

Table 9. PVC Pipe Thermal Expansion (in.)

Temp.
Change

ΔT
(°F)
Length of Run (ft.)
10 20 30 40 50 60 70 80 90 100

30

0.11 0.22 0.32 0.43 0.54 0.65 0.76 0.86 0.97 1.08

40

0.14 0.29 0.43 0.58 0.72 0.86 1.01 1.15 1.30 1.44

50

0.18 0.36 0.54 0.72 0.90 1.08 1.26 1.40 1.62 1.80

60

0.22 0.43 0.65 0.85 1.08 1.30 1.51 1.73 1.94 2.16

70

0.25 0.50 0.76 1.01 1.26 1.51 1.76 2.02 2.27 2.52

80

0.29 0.58 0.86 1.15 1.44 1.73 2.02 2.30 2.59 3.24

90

0.32 0.65 0.97 1.30 1.62 1.94 2.27 2.59 2.92 3.24

100 0.36 0.72 1.03 1.44 1.80 2.16


Now, the temperature rating of PVC at 70ºF is higher than you might think, but I suppose the plumbing codes are based on the assumption that 140º might often be seen, and therefor PVC would simply be inappropriate in the house.

Temperature and Pressure Ratings
Thermoplastic piping materials increase in tensile strength as temperatures decrease, and
decrease in tensile strength as temperatures increase. This characteristic must be considered
when designing piping systems with PVC material. To determine the maximum pressure
capability of each PVC piping product, temperature correction factors have been established.
To determine the maximum suggested pipe operating pressure at a particular temperature,
multiply the base pressure by the correction factor (see Table 6 and Table 7).
Table 6. Schedule 40 and 80 Pipe Pressure Ratings (psi at 73°F)
Nominal Pipe Size (in.) PVC 40 PVC 80
½ 600 850
¾ 480 690
1 450 630
1 ¼ 370 520
1 ½ 330 470

2

[harrymusgrave]

The temperature here ranges from approx. 60 - 90 at the extremes, 60 being a cold night in the Winter and 90 being a very hot day in Summer. Low to mid 80's are the normal daytime temp. I am at 100 ft elevation. Upslope, it gets cooler.

I already asked the "Master Plumber" at HD weeks ago and he indicated it was okay, but yesterday I wanted some clarification and he seemed to change his opinion about the PVC, saying CPVC or copper would be acceptable. I presume we had a miscommunication. So, I wanted to ask other plumbers about the PVC. The information Jimbo provided gives a clue as to why PVC might be frowned upon. Usually there are good reasons for specific building codes.

A couple of years ago I had a problem with some CPVC pipe hooked up to a well. The pipe seemed to encourage, or at least not discourage, growth of some bacteria that made the water smell bad. I live on the side of a volcano. There is lots of sulfur here and this bacteria does something with the water and makes it smell like rotten eggs. I called the well driller and he said he has heard of this happening and tried to resolve it with some customers by shocking the whole system with chlorine. He said he was only partly successful; the smell kept coming back. In my case, the problem worked itself out after a long time - perhaps a year. That is why I want to avoid CPVC. I think something in the plastic has an affinity for that bacteria.

Since the well water is not chlorinated, and the CPVC would be before the UV, I fear another episode with this mystery bacteria.

Thanks for all your input...

[Gary Slusser]

Sch 40 PVC has been used for decades outdoors and under houses and from wells into the house (usually a basement) across the US from the east coast to the west coast. That's for both potable and irrigation waters. In 24 years I have never heard of pressure busted PVC in residential use and IMO that's because most well water systems use pressures no higher than 65-70 psi and most have a PRV set at 75 psi. So Harry, I doubt there would be a pressure rating reduction serious enough to cause any concern.

Your odor problem could be naturally occurring H2S gas or a number of different types of bacteria; iron, manganese or sulfate reducing types, or Coliform bacteria. A UV light is a poor choice if you have any type of reducing bacteria because it won't work well or long plus UV can not be used with any H2S gas in the water. Or if the water hardness, iron, manganese etc. is higher than the low minimums that are allowed.

A much better choice is a disinfectant like chlorine or ozone. Hydrogen peroxide doesn't always work for reducing types of bacteria. Following the disinfectant would be a carbon filter for chlorine and to remove not only the chlorine and its taste and odor but any 'sediment' that was caused by chlorine etc. converting iron and manganese and H2S into particulate matter.

[harrymusgrave]

My vote is for sulfate reducing bacteria that colonized a length of CPVC pipe. Coliform is possible, but in a 100 ft deep well? I was able to isolate the smelly issue to a length of CPVC pipe. There was no smell in PVC or copper runs from the same well. Not concrete proof of anything, but suggestive enough to me along with the driller's anecdotes that I want to avoid CPVC.

You say UV is no good with sulfate reducing bacteria? Can you please explain interaction of UV and H2S ? Since we can't smell anything, I assume we don't have any bacteria now.

The info I want to obtain is whether PVC can be used from the pressure tank to the UV and pass inspection.

So far I sense a "maybe, maybe not".

My opinion, which is not worth 2 cents in this field, is that PVC is perfectly adequate for this purpose. You are right, my pressure is never more than 60 psi and the temperature under the house is rarely above 80, so the pipe should work just fine. But I want to pass the plumbing final inspection, so I have to do things with that in mind.

My wife has informed me she was witness to the HD "Master Plumber" telling me to go ahead and use PVC up to the UV. And I did. And now I wonder if I need to rip out what I've done

[Gary Swart]

While PVC would not be my choice for material, it is my understanding that PVC should not be exposed to UV rays. Buried, it should be fine. As others noted, the pressure your water system will create will not be a problem. It should never be used for compressed air both because of the higher pressure and UV ray exposure.

[harrymusgrave]

Gary - a very good point about UV. If I attached a PVC fitting to the input port of the UV chamber the fitting and some pipe would be exposed to reflected UV.

[Bob999]

The info I want to obtain is whether PVC can be used from the pressure tank to the UV and pass inspection.

Most codes allow use of PVC for "supply" systems but not for "distribution" systems. With a well the line between the supply system (the well) and the distribution system (in the home) is not specifically defined. If the job is subject to inspection it is imperative to consult with the inspector to see how local regulation/practice defines the line between the supply system and the distribution system.

[Gary Slusser]

My vote is for sulfate reducing bacteria that colonized a length of CPVC pipe. Coliform is possible, but in a 100 ft deep well?

It doesn't matter what type of reducing bacteria caused the odor because all are harmless. Coliform indicates the probably of harmful bacteria.

The depth of the well has next to nothing to do with bacteria contamination but 100' isn't a very deep well, it's actually fairly shallow. My record is a few months old 605' well that had Coliform in it and was found only after the family moved in to their new house and their month old infant was very sick and the doctor mentioned testing their water again.

Bacteria live anywhere in the earth that is not too hot for them to survive and then, as we see with black smoker vents on the bottom of the oceans, with water temps to as high as IIRC, many hundreds of degrees F, some types of bacteria thrive there anyway.

The odor you smell is from the digestive gas the bacteria produce, not the type of tubing/pipe that is used. The gas is dissolved into the water and as soon as you open a faucet the water is depressurized and aerated causing the release of the gas into the air and you smell it.

I was able to isolate the smelly issue to a length of CPVC pipe. There was no smell in PVC or copper runs from the same well. Not concrete proof of anything, but suggestive enough to me along with the driller's anecdotes that I want to avoid CPVC.

See above but, bacteria can grow and create colonies anywhere in the water system. Including in copper or SS tubing.

You say UV is no good with sulfate reducing bacteria? Can you please explain interaction of UV and H2S ? Since we can't smell anything, I assume we don't have any bacteria now.

You should not assume no Coliform because you usually can't smell and you can never taste it.

All the things I listed previously, and especially reducing types of bacteria, cause a coating on the outside of the UV light's (clear like glass pipe) quartz sleeve that the lamp is inside of and the coating blocks the transmission of the invisible UV light from penetrating it so the light can't get into/through the water inside the UV chamber. You may as well unplug the light 'cuz all you're doing is wasting electric and feeling good thinking the light is working but there is no 'deactivation' of the bacteria in the water.

Reducing types lay down a slime on the quartz sleeve, H2S gas, hardness, iron etc. causes a sediment to form on the quartz which prevents the light from getting through. Which reduces the time between scheduled maintenance and thereby increases maintenance of the light. As little as a fingerprint on the lamp or the quartz blocks transmission also.

The info I want to obtain is whether PVC can be used from the pressure tank to the UV and pass inspection.

So far I sense a "maybe, maybe not".

My opinion, which is not worth 2 cents in this field, is that PVC is perfectly adequate for this purpose. You are right, my pressure is never more than 60 psi and the temperature under the house is rarely above 80, so the pipe should work just fine. But I want to pass the plumbing final inspection, so I have to do things with that in mind.

My wife has informed me she was witness to the HD "Master Plumber" telling me to go ahead and use PVC up to the UV. And I did. And now I wonder if I need to rip out what I've done

I agree and as far as I can see, if you are having the installation inspected, you need to get the local inspector's interpretation of the code there.

But, it is still a free country and millions of feet of PVC is in use outdoors in sunlight on well and irrigation systems unprotected from sunlight or the UV light in sunlight. Plus you are not 'distributing' your water until after the water treatment equipment. You are also not inside the foundation or inside the house.

If it was mine, I'd use 1" sch 40 PVC. I have also used it on UV lights with a flow control button in the inlet, for over 20 years with no known problems and my name and phone number is on every one of them so I think I'd hear if there was a problem with a flooded basement etc.. But I am not telling you what to do other than to talk to the local inspector if you are having an inspection.

BTW, that 75 psi PRV I mentioned is code everywhere but many people don't install one because if it pops, they are usually not plumbed to get rid of all that water from flooding the place. And in 14 years on the internet and 23 years in water treatment and pump and pressure tanks, I've never heard of one having popped yet.