Rainwater plastic smell after pumping - degrading poly pipe?

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Rainwater plastic smell after pumping - degrading poly pipe?

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Started 7 years ago by Cloudy
Latest reply from Diver

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Cloudy
Member

On our farm we have rainwater tanks that are gravity fed to the house by underground poly piping. This has been in place for 50 years. The large two cement tanks are up the slope at the shed. We also have a small 15 year old poly tank attached to the house. When this fills, a pump automatically sends it up to the shed tanks.

Here is a diagram: https://www.dropbox.com/s/ynjra2z7v15cegd/Rainwater%20tanks.jpg?dl=0

Due to the age of the cement tanks, the inlet and outlet is the same, about 10cm from the bottom. Not ideal I know but the tanks are relatively clean.

This smell happens straight after water is pumped up. Usually after a period of no pumping (ie. in summer). During winter when the water is being pumped up more often the smell is not as bad. It lasts a day or two. Worse in the shower as heating the water in the hot water system seems to increase the smell. Same as with the kettle.

To resolve it I would swap to the other shed tank (which wasn't being pumped into) as soon as the pumping finished. This did fix the issue.

This has been going on for several years until last year when we got three large filters installed (carbon and 1 & 5 micron) plus a UV filter. All done by a professional installer. It was positioned on the pipe leading into the house, in other words, after the tanks. It did seem to stop the smell. But after a dry spell earlier this year, the smell still came through, quite strongly. Strange thing was, those little cheap tap filters (you get from Bunnings) were able to stop the smell completely.

So I got the installers back in who were really puzzled. They checked it all over, tasted the water directly from the tanks, looked over the pipe work and could not see any issues. The filters were clean suggesting that our rainwater is very clean. They replaced the filters anyway. I pumped some water up and found I couldn't smell anything. Seemed to be working. However this was not after a dry spell. They said if I get it again to call them.

After the recent rain in Perth (after a dry spell), the pump kicked in and I had the smell back for a few days.

Just a side note, I have had the water tested for microbes etc and the results are fine.

Any thoughts on what is the cause of this smell/taste? I'm concerned it is the degrading of the insides of the poly pipe which is exacerbated by the pressure of pumping. However I cannot find any information on this and the testing lab hasn't heard of it either in this setup. It is unusual as we don't use any chemicals in the water and the pipe is underground.

I'm hoping to have the water tested for polyethylene leaching soon.

Cheers

Posted Friday 5 Dec 2014 @ 12:00:05 am from IP #
David
Member

I hope it's not PVC piping, I would really hope it's polyethylene in preference, I've been using tank water for quite a long time now never had anything like that. Do you use a "silver" carbon filter? I don't use a UV light on the system, never found it was needed for rain.

Maybe taking water via floating pickup maybe a better option the water near the surface is always the best water in a tank, lack of oxygen in the water at the bottom. Sometime back I was conducting testing on how to improve water quality in tanks I found if the water is circulated from the bottom and back to very top during the day (solar pumps) then water quality improved dramatically, not filtering just a significant improvement in aeration of the water, a bit like a clean stream has really nice water. In any event it is much easier to simply use or make a just below the surface floating pickup system as it does not require anything electro - mechanical to operate and wear out, done it that way ever since.

Is it possible your getting a sort of micro shedding of material from either the pipe if it is PVC or from the pump impellers maybe, assuming it is plastic.

Posted Friday 5 Dec 2014 @ 12:55:11 am from IP #
johnmath
Member

I doubt that the smell is from the poly, although I believe there are other good reasons for not drinking water stored in poly tanks. (I have a separate galvanised tank which is fed through copper pipe purely for drinking water.)

One thing to note is that activated carbon filters do eventual "fill up" and slowly stop working, which might explain why they worked well at first but seemed to not work so well later. The activated carbon cartridge needs to be replaced at suitable intervals.

At my house I have six tanks in series connected by underground poly "ag" pipe (green stripe) except for the last 10 meters or so from the closest tank which uses poly mains pipe (blue stripe) because it is under suction.

When our tanks are low, I switch to mains water, which feeds in from the street end of the house plumbing. On the other hand, the rainwater pump feeds the house into the far end of the plumbing. When we are on mains water, rainwater sits stagnantly in the feed pipes and the pump.

When I switch back to tank water after a spell, for a short time there is a very pungent smell from the water that has been sitting in the pump, which dissipates in a few seconds. I believe this to be because rainwater is slightly acidic, due to dissolved CO2, and the acidity (combined with a lack of minerals - see below) is corroding the internals of the pump.

I suspect you may have a similar issue where the stagnant water from your pump is contaminating the tanks when it transports water to the tanks after a dry spell. When I replace my pump, I will try one that is stainless steel, not cast iron.

I have read that the increase in atmospheric CO2 concentrations due to anthropogenic fossil fuel burning is significant in raising rainwater acidity and the corrosive effect that rainwater has. I measured my rainwater at ~6.3 pH. I recently picked up some limestone rocks and put one or more in each tank. The pH has since risen to ~6.8-7.0 (it's a bit hard to determine exactly with my test kit). I have yet to switch back to rain water after a spell on mains to determine if raising the pH closer to neutral 7.0 makes a difference.

It is interesting to note that reverse osmosis desalinated water from desalination plants is considered corrosive due to its inherently low mineral content and is not suitable for distribution through municipal networks without post-treatment (re-mineralisation).

Rainwater is likely to have very low mineral content. I assume that the rocks I have added to my tanks will also add some dissolved minerals, but of course this is all very unscientific.

Another possible consideration is that anthropogenic pollutants from a range of sources are likely to be present in rainwater. Are you near any significant source of pollution?

Posted Friday 5 Dec 2014 @ 12:56:00 am from IP #
Cloudy
Member

David said:
I hope it's not PVC piping

Sorry, not sure why I said that. It is only black polyethylene piping. I've heard of the float idea. Just not sure how it will go with pumping water through it at high pressure.

I doubt it has silver in my filter, it is just a standard carbon block.

johnmath said:
One thing to note is that activated carbon filters do eventual "fill up" and slowly stop working, which might explain why they worked well at first but seemed to not work so well later. The activated carbon cartridge needs to be replaced at suitable intervals.

Yes I did find that my 1st particle filter (5 micron) was quite packed up but the granular carbon and 1 micron I believe were fine. I replaced them all anyway (changed the carbon to a block type) and the flow was much better. This seems to indicate organic matter from the tank or biofilm inside the piping coming through. However, points that go against this are:
1) My folks live on the same farm and have a new house and metal tanks but have the same filtration system. Their filters were more packed up than mine. The 5 micron looked the same dirty colour however they did not have any smell in their water.
2) When the smell occurred earlier in the year, my filters were inspected and they did not appear clogged at all (they were under a month old).
3) The last filter, 1 micron, was not clogged.

What confuses me is how the colour of the water changed slightly with the smell. Not very noticeable but definitely a slight yellow/grey discolouration occurred in the water which went away with the smell.

The 10m length of pipe between the house tank and the pump is the only place stagnant water sits. I don't see how this is enough to pollute a 50,000L tank. Furthermore, the filters should have resolved this.

I am not near any source of pollution and the farm is over 200 acres surrounded by bushland and small farms of little activity.

Posted Friday 5 Dec 2014 @ 2:01:53 am from IP #
Solgen
Member

In our house which uses a combination of tank and mains water that if we go away for a period (say 4 weeks) when we return our hot water has a distinctive smell. I have now worked out the problem. Our kitchen sink is fed by a pipe (copper) off the main hot water main but we rarely use the kitchen hot water tap, using a bucket from the hot water tap in the laundry, a shorter run and less waste of water. What is happening is the water is stagnating in the hot water pipe and potentially legionella bacteria are also growing there. We now turn on the hot water tap in the kitchen at least once a week to clear out this buildup of stagnant water, this seems to have cured our problem.
Cloudy, do you have potentially any dead-legs in your plumbing system that could be causing your problems.?

Posted Friday 5 Dec 2014 @ 3:51:50 am from IP #
David
Member

My filtering order is, 20 micron, 5 micron, Silver impregnated granular activated carbon filter refillable cartridge, uses about 2kgs of material for each refill I bought two so I just change them over, then clean and refill the one removed from service. I change over every 12months, the pleated filters keep most of the dirt out of the carbon filter and the "silver" stops the bacteria breeding cycle in the carbon filter, Town water typically has chlorine or similar in it so does not require something to stop a bacteria cycle in them, tank water does not have chlorine of course, that's why I use a "silver" impregnated cartridge.

Float pickups, I made mine they vaguely look, sort of like mushrooms or lily-pads for want of better way of putting it, they don't care if the water comes in at high speed simply goes down into the tank.

Posted Friday 5 Dec 2014 @ 6:16:06 am from IP #
Diver
Member

Cloudy said:
On our farm we have rainwater tanks that are gravity fed to the house by underground poly piping. This has been in place for 50 years.

Is the 1.5 inch black poly pipe an outside or inside diameter?

Pumping flow rates?

You can work out a pipe's flow velocity at a known flow rate provided you know the pipe's internal diameter (ID).

How far off the bottom of the poly tank is the pump draw valve?

Has anything on the roof catchment area been altered?

Modern polyethylene is a non porous inert food grade material that should last for over 100 years.

50 years puts the pipe's 'birthday' in the early 60s. I would speak to someone of knowledge like Timon Visser, Product Development Manager, EnviroFLO Systems Ltd or someone who works in a technical position with a poly pipe manufacturer, explain the smell issue and ask whether the composition of polyethylene has changed since the early 60s and whether it is possible that the material is leaching. Just explain briefly your query with the girl who answers and she is sure to put you in contact with a very knowledgeable person and they should enjoy the question.

Rainwater is also naturally acidic, be sure to mention this. Have you ever tested the pH?

Posted Friday 5 Dec 2014 @ 2:03:16 pm from IP #
Chip
Member

Maybe the smell comes from the poly tank at the house. If some water sits in it for ages then the very top of the water will be heating up and this, added to heating of the tank above the water line (especially if the sun strikes it directly) could speed up the degrading of the tank and the absorption of odours into the water. Some may be transferred to dust particles which will add to the problem plus extend the time before it clears.

You might be able to reduce heating of the tank by shading it or painting it white and also by maximising the amount of water that sits in the poly tank for long periods eg by pumping less water more often so that there is more thermal mass left to stabilise temperatures.

Water left for ages even in a food grade drink container will gradually develop an odd odour and taste but is probably not a health issue though testing and advice is a good option for your situation.

Posted Friday 5 Dec 2014 @ 10:11:21 pm from IP #
Cloudy
Member

Solgen said:
Cloudy, do you have potentially any dead-legs in your plumbing system that could be causing your problems.?

Interesting thought but no. Even if we did, it wouldn't make sense as it only happens after we pump.

David said:
My filtering order is, 20 micron, 5 micron, Silver impregnated granular activated carbon filter refillable cartridge,

I wonder why my installer placed the carbon in the middle? You would think it would go at the last stage. How much does your carbon cost? I'm not sure if I can refill mine being 20x2.5 size filters.

Diver said:
Is the 1.5 inch black poly pipe an outside or inside diameter?

Outside

Pumping flow rates?

~130 lpm and flow velocity of about 1.8 metres per second. Bit fast I know.

How far off the bottom of the poly tank is the pump draw valve?

70mm

Has anything on the roof catchment area been altered?

No.

I would speak to someone of knowledge like Timon Visser, Product Development Manager, EnviroFLO Systems Ltd

Will do, thanks!

Rainwater is also naturally acidic, be sure to mention this. Have you ever tested the pH?

Using a basic test kit, I found our rainwater to be more or less the same as the stuff falling straight out of the sky. About 6 pH. I took the samples directly from our gutters, tank and finally through to the house taps. No change. But I haven't taken the pH of the smelly water so that is a good idea as I know pH is raised with more organic matter content.

Chip said:
Maybe the smell comes from the poly tank at the house.

It is a good thought but immediately after the tank was pumped (which I then got the smell) I took two samples from the left over water from the poly tank. One clean and one dirty (stirred up some of the organic matter on the bottom of the tank into it). No taste or smell evident, even after boiling it up.

Just want to thank everyone for throwing in their advice, really appreciating it

Posted Saturday 6 Dec 2014 @ 1:58:22 am from IP #
Diver
Member

The pipe's ID could be around 38 mm but I can only guess on the wall thickness. If it is let's say 2 mm, then the pipe would hold not much more that 1 litre per metre. This is a velocity of about 2 metres per second. 1.8 metres per second would be for a 40 mm inside diameter.

The water moves in boundary layers (streamlines) and the water next to the wall moves very slowly. 2 metres per second would give the pipe a clean out but it wouldn't scour it as that requires bubble flow.

Having the tank's draw valve 70 mm above the bottom of the poly tank is low considering the draw velocity but the water is going to a large tank and not directly to the house and so it wouldn't usually present a problem. All the same, the pumping flow rate is high and you are better off if you can pump to one tank and then let it decant for a few days before doing a gravity transfer to the other concrete tank that supplies the house.

Did you have anything done to the pump around the time that you first started having these issues?

I will wait until you find out about your vintage of poly pipe before surmising anything but you could try adding a liquid oxygenator and dosing some Epsom Salts to the poly tank to see if that helps. That way, the treatment would travel through the whole system. If there is still a smell, then the aging poly pipe could be the culprit.

Posted Saturday 6 Dec 2014 @ 3:02:05 am from IP #
Diver
Member

Revisiting this old thread. I spoke to a very knowledgeable technical person at a poly pipe manufacturer and he said that if poly pipe passes through an area that is for example used to wash or de-grease machinery parts, hydrocarbons in the soil can leach through the poly pipe.

Posted Friday 27 Jan 2017 @ 8:50:45 pm from IP #

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