We have 2 concrete tanks 15,000 each. The first seems to catch the sediment the second I can easily see the bottom and only has a few insects at the bottom. It is at least 2.5m deep. Both tanks a full. The House Roof catches the water and is feed through downpipes straight into underground pipes and into the tanks.

We have a Rheem hot water system (with heat pump, and magnesium Rod), which is used for showering/washing dishes etc. Not for heating the house.

Pump house and tanks are only a few meters from the house. Roof is very clean just small bush over hanging (it is being removed). There is no gutter or down pipe protection. There was no filter in the filter housing so the water has been pumped into the house directly. The filter housing has only 1 filter (now fitted with wafer filter, I think we need more). The kitchen sink is the only house outlet with a small carbon filter.

The smell from the Taps (both hot and cold) is not exactly like rotten eggs nor musty, but basically smells like cow dung Sh!t3. I took a sample of tank water and it does not smell. Tank water is tested and has Coliforms, but no e-coli. Hot tap seemingly had no Coliforms??? weird seen as filter did not exist, maybe the 50degree+ heat destroyed them???

We wish to cleanse the system and remove the smell and possible contaminants. What should we do to cleanse? What should we do to the system going forwards, to prevent it happening again?

  • Cover the access hatch and overflow outlets to stop animals falling in. Commented Jan 22, 2021 at 8:18
  • Please feel free to edit your post to fix all the typos. That will make it much more readable and clear. What do the gutters have to do with your water supply system - are they feeding rainwater into your holding tanks? What does the hot water system have to do with it - is this supplying domestic hot water? Is it supplying hot water for heating? The more clear you can be, the better the answer you'll get.
    – FreeMan
    Commented Jan 22, 2021 at 12:22
  • We had a similar (no identical, but similar) come up here a few weeks ago. Here is a link to my answer: diy.stackexchange.com/questions/213087/… Commented Jan 22, 2021 at 15:48
  • Edited. amd clarified. Commented Jan 24, 2021 at 22:59

3 Answers 3


The smell is hydrogen sulfide . Causes are bacterial action in decomposing organic material or bacterial action breaking down inorganics such as sulfate. One can smell less than a ppm of H2S. It is not harmful at low levels where it can easily be smelled. In any case the bacteria need to be killed . Bleach (chlorates ) is the most common way to do that ; it needs to be controlled to not add other smells to the water.

  • Also, seemingly the magnesium rod in hot water system (design to prevent corrosion) can also make hydrogen sulphide gas, most likely not my main problem as we have both taps with the smell, although the has a more intense smell. Seemingly replacing with an aluminium rod removes the smell. Commented Jan 24, 2021 at 23:06
  • the hot has a more intense smell, but that could just be because it is hot water which has steam??? Commented Jan 25, 2021 at 10:03

A rain collection system will always have organic matter in it, mostly from bird crap and leaves on the roof.

If it's conventional asphalt shingle roof it will also have various petrochemicals in it.

One way to reduce this is to throw away the first 50 gallons of every rain event.

  • Take a 45 gallon food grade barrel. Remove the top.
  • Near the bottom drill a 1/2" hole and stuff it with a synthetic sponge.
  • Cut a disk of styrofoam to fit inside the barrel.
  • Put port in the top of the side of the barrel and connect to your cistern.
  • Install a screen over the port.
  • Screen the top of the barrel.
  • Allow the roof water to fall on the screen.

In normal use this is what happens.

  • it starts to rain.
  • The barrel starts to fill.
  • As the barrel fills the styrofoam disk floats. Water coming thorugh has to flow around the disk.
  • Once the water level reaches the output port, water flows out the port, but the disk still separates the initial dirty water from the later cleaner water.
  • The sponge in the bottom leaks, and over the next day drains the barrel for the next rain event.

Tuning: Smaller hole/tighter sponge slows down the reset. May want to do this if you get frequent light rains.

Maintenance: Clean the screen when you pass them. Clean the port screen 2-3 times a year.

A system like this is still asking for trouble. Dead squirrel or bird on the roof? Yuck. I would consider either a chlorine system for the tank, and bring in your drinking/cooking water from an outside source, or at least putting the kitchen cold water tap on a UV sterilizer lamp.

Here we can send a water sample to public health for either a bio-contamination test (coliform bacteria) or a chemical test (crud in the water) I would suggest doing a coliform test with the first batch of water after a long dry period, and a chemical test whenever some major aspect of the system has changed. New roof, new tank, new sealant somewhere.

If it's a shingle roof, when time to replace consider a metal roof instead. Asphalt is worst for leachates during the first year or so.

  • This is a very clever idea, Thank you for sharing. Commented Jan 24, 2021 at 22:57
  • Could you expand on the leachates theory a little more. I am researching our roofing material. It has a stone chip finish on a zincalum/painted steel, but it is a modern product, but I do not know the actual product used. Commented Jan 25, 2021 at 10:16
  • @NZDev I discovered how toxic shingles were when I left some on the grass. Two days later I picked them up. Grass was yellow. Took months to recover. You need to research what the stone chips are stuck to the metal with. But quick tip: Does it smell? Lots of volotiles have reek. No smell doesn't mean safe, but a smell really means check. Note that rough surface will trap dirt. Also a galvanized roof may release zinc. Harmless in small quantities (You need some zinc) Easy to test for. Commented Jan 26, 2021 at 17:16

I would call a water treatment company like "Culligan " or a local water treatment company and have them tell you what equipment you need to make this water safe for drinking.

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