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