We moved into a brand new build and within 3 months our water tank from roof supply was contaminated. Our water stunk and after getting it tested it was high in ammonia and sulphide. We emptied the tank, got it scrubbed out and filled with town water while we were sorting out the source of the contamination. When we moved in the gutters and down pipes had nothing to stop leaves or anything going down there, or a first flush system, as our plumber advised we didn't need anything. Luckily we did have filters and a UV system.
We got cameras sent down our pipes and our pipes blasted and we now have a first flush and leaf slides.
9 months after contamination, we switched our water back on and 3 weeks later our water smelt again and we are now contaminated again!!! High ammonia again!
$10,000 of paying for water and plumber bills and no one can tell us what is going on!
We are desperate if someone has some insight as to what a cause could be or advice for our next step.
You seem to have a high level of microbes in your water as high ammonia levels come from decomposing (even micro bacteria decompose). - as you probably already know.....
Filters in front of the tank to get rid of any crap in the rainwater is the right first step, but you probably still got bird poo and other fine particles in the water. I recommend to use regularly Hydrogen peroxide as it is antiseptic and kills all microbes, it dissolves quite fast (about 3 hrs for our 25k liter tank) and its way better for the environment than chlorine. - its also cheaper....
I hope that helps a bit. - good luck finding the source of evil
Make sure you clean out your first flush on a regular basis. The water can get putrid in there and leaves can block the outlet. We usually leave our tap on and have a half inch garden hose on it to carry the water away. I periodically remove the cap and flush out with another garden hose. Just be very careful undoing the cap, as if there is any water being held in there, it will rush out with unbelievable force and you will likely wear the lot! (OH made that mistake. it was quite funny )
It seems to be happening on roughly a 12 month cycle, so could be bird poo. The sparrows here are frantically setting up house under the eaves and in the guttering, the starlings and blackbirds seem to be sticking to nesting in the shrubs thankfully.
Or a buildup of dead leaves over winter that are now breaking down with the warmer temperatures.
In auckland city, and I suspect most places, a first flush is compulsory now.
Was talking to my plumber about it today to see if I should flush as its so long since we have had rain and he said its only necessary in summer to flush as in winter it tends not to get putrid
Depending on how far your tank is from your house, you pipes will hold 3-500 litres of water between the house and the tank so when you do your first flush, as stikki says there is a lot of water to come out, and fast