With regard to rainwater tanks can anybody explain how the following statement, that I read in a Ministry of Health publication, be true. "It is best to use small tanks run in series instead of one large tank, since as the water passes to successive tanks the microbiological quality improves significantly."
ralphdog1,
Mar 24, 10:03am
Complete guess but maybe because fresh water has significant microbiological activity, and that level decays as a function of time. Fresh water effects the water you consume today if you have one tank. Several tanks in series means the water you are using is the oldest, therefore the microbiological activity level has had time to decay?
phalanx2,
Mar 24, 10:39am
Sediment settles to the bottom of the tank, the top overflows to the next tank and any sediment settles, and so on.
Each successive tank acts as a trap for sediment and each in series has less passed on to it.
If using for drinking water, maybe fit grills to keep the leaves and small critters out.
ira78,
Mar 24, 7:57pm
In theory that is probably accurate. In practice everyone uses 1 or 2 large tanks. A pair of 16,000L tanks is much more practical and cheaper than seven 5,000L tanks.
And you can throw sediment and UV filters on it if you're worried.
seafield1,
Mar 24, 8:05pm
We have only ever used one very large tank. Never had a problem. We do make sure that the roof is cleaned regularly and we have gutter guard over the guttering to keep out the leaves etc.
tintop,
Mar 24, 8:31pm
Yep - I am with this, a very good idea if you can make it work in a practical fashion. Problem lies with a drought situation, you will need to be able to draw on the second to last tank etc, when the end one runs dry.
Our last place had 3 X 11,000 l tanks, all independently fed by different roof areas. Water was taken off at the bottom of the tanks. I cleaned them all out one by one after about 10 years of use as part of the preparation prior to selling.
Perhaps a 100 l of mud in the bottom of each. :) But we survived!
wasgonna,
Mar 24, 8:56pm
Gutter guard may keep the leaves out but what about the bird shit off the roof, or is that what people refer to as "sediment"?
crackerjack19,
Mar 25, 3:18am
I have lived with and used tanks that had not been cleaned out for years and our family never had any illness that needed to be analysed as to the safety of the water. As soon as was possible the tanks were cleaned out and pollution of the water by debris was cut back as much as was possible. We also installed filters on all lines that were possibly used for drinking water.I prefer roof water/rain,to any, other than deep bore water. My extended family used well water for many many years without any of the problems we subsequently had with town supply.
bluefrog2,
Mar 25, 3:35am
I'd go with this explanation too. As rainwater flows into the tank, it could stir up the sediment at the bottom that contains all the pathogens, so drawing off water from a second tank with a controlled flow taken from the top of the first tank makes sure water coming out of your house tap is only taken from the cleanest layer of tank water. In practice, I've never seen water tanks in series like that - it would take up too much space. So one well designed, large water tank thats well maintained probably works perfectly well.
ira78,
Mar 25, 6:08am
It puts hair on your chest!
So, women beware.
5425,
Mar 25, 6:30am
Check the teeth of kids on farms without Fluoride and then the rotten teeth of most town kids with Fluoride.
tintop,
Mar 25, 7:01am
How about starting you own thread on the subject ( even though it has been done to death) - why hijack someone else's ?
socram,
Mar 25, 7:22am
OP hasn't stated whether the rainwater would be used as drinking water; supplying toilets/washing machines; or the garden!
I have been thinking about a tank or two for the garden - but not in series - in different locations, but taking the water off from the lowest point to avoid sediment build up.
tintop,
Mar 25, 7:39am
Same - got our water bill for the period over the drought - and the new planting.
bill1451,
Mar 25, 8:32am
Now available are whats called floating take offs, these are on a flexible hose and take water off the top of the tank, another trick is to have an upstand of say 2 or 300 mm in the bottom of tank so no sediment enters the outlet
mack77,
Mar 25, 9:33am
Thanks everybody so far for your helpful comments, but what I failed to mention that in this Ministry of Health document is that they stated "always draw the water (household) from the top of the water tank. I thought that all the harmful microbiological organisms like faecal bacteria, protozoan cysts (eg giardia, cryptosporidium etc) and viruses (from faecal material) would be evenly distributed throughout the water or are they more concentrated in the sediment as ''bluefrog2'' states. However even if they are more concentrated in the sediment, I would have thought that the water that you transfer from the large tank to the small tank will contain the same no. of micro-organisms per litre of water as that of the large tank. Do they keep increasing in no. as time goes on or are the no.s in the tank simply equal to the total no. that have entered the tank via the contaminated rainwater supply? Is my thinking astray?
socram,
Mar 26, 9:07pm
Agree with #16. I would have thought that some form of filter before entering the tank would make some sense too. Even in town water, if you leave it around for any length of time, it is surprising what is in there, but good point mack77.
nzdoug,
Feb 21, 5:48pm
We treat our tank water w "Pour N Go".
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