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solar powered rainwater tank sterilizer


Bruce Tuncks
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I've just made one of these for myself. It consists of a UV sterilizer ( 4.5 liters per min ) operating at a conservative 1 liter per min.

It is sold as a caravan 12 volt thing.

I have coupled this to a 12 volt pump and a 12 volt solar panel. The box sits near the tank outlet and has 2 pipes. One sucks from the bottom of the tank and the other delivers the uv treated water back into the top of the tank. At 1 liter per min, it would take 2 weeks ( full time ) to pass 20,000 liters through. 

Hopefully, this would be a "fit and forget" addition to a rainwater tank with the benefit of making the water safer for drinking, well at least after it had been operating for a week or more.  Dilution of bacteria etc helps even if there are still some present.

Now the motive for doing this was just so I could drink the water without worrying, but here is the question... would some customers pay $750 for such a setup?

Any comments? A pin to prick me just right would be good in the long run if there is nothing commercial in the idea.

 

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Hey Bruce,

 

We live on rainwater and rely on filtration for cleaning.  So there's the filter on top of the tank (mosquito mesh size) which keeps out the bigger nasties, then under our kitchen sink we have a double filtration system like this: https://www.psifilters.com.au/standard-twin-undersink/10037-1685951-psi-300s-with-pentek-cbr2-10-carbon-cartridge.html#/1-would_you_like_to_buy_additional_cartridges_now-no_thanks_no_charge/13-connection_fitting_option-1_2_inch_flick_mixer_braided_line_fitting_no_charge/17-faucet_standard_options-model_a_standard_long_reach_nsf_faucet_no_charge

 

So for showers, hand washing, dish washing and laundry there's no filtration apart from the tank inlet, but for drinking water / kettle / ironing etc we use the little tap connected to the filters.

 

There might be a market for a sterilizing system like that, but personally I wouldn't buy one.

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I have been on rainwater for over 50 years and all I use is the screen on top of the tanks to exclude mossies. I also syphon off the sludge that gets in the bottom of the tank, if and when we get decent rainfall. Have not had a problem yet. The only thing I miss out on is fluoride in the water for my teeth, but as i still have excellent teeth at 84 years old I think I may be able to last without it.

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Thanks Marty, yes there are some bigger organisms like cryptosporidium  which need a bigger dose of UV to kill so a filtration system would be a good idea but would add to the cost.

My son says nothing is needed. It is difficult to know since any advice would be tainted by fear of litigation on the part of the adviser.

Just imagine you are the adviser... you would feel it safer if you maximised the risk . Just like flying into clouds, the official advice is so far from the truth that it is not much good at all.

BUT I do know a guy ( from Berrigan, way north of here ) who pooh-pooed the idea that tank water could be unsafe till he got some awful disease.

Do you ever get your water tested? 

 

 

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Here's a suggestion. You can make better decisions with more data. At this stage you only have financial data, which is the bottom line in a sales process.

 

Why don't you take a reasonable sample of your tank water (say 200 litres) and from that sample take a random sample of about one litre. Send that sample off for microbial analysis to see what the unpurified water contains. While the sample is away, run the purifier for a period that you consider is sufficient to properly treat the 200 litre sample. At the end of that time, take another one litre sample and send it off for analysis. The two analysis reports will tell you how well or otherwise the purifier works. Then you have some data to show why people should make the financial outlay.

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I'd have to say no. We use a double filtering system on the mains water, and it comprises a 1 micron spun polyester filter and a 0.05 micron activated carbon filter, both of which provide a very good filtering system that stops virtually all of the bad bugs - and which system improves the taste of the water enormously, as well. The whole system costs less than $300 and I replace the filters annually at a cost of about $35 for the two filters.

 

The filtering system has been in place for over 15 years and the only problems I've encountered were a couple of cracked PVC fittings, and a white PVC filter housing that cracked due to inadequate UV protection. I replaced the cracked housing with a blue-coloured one for less than $25, and it has been trouble-free since.

 

The only way you could garner sales with a UV steriliser is by providing lab-quality test results that shows your system produces better results than simple filtering through activated carbon. Remember that filtering through activated carbon is a standard military water-supply system technique, that is regarded as producing highly acceptable water-quality levels.

I speak as a former military engineer who was regularly involved in setting up watering points for troops, where local water supplies were seriously contaminated with bugs or undesirable minerals and toxins.

 

EDIT - I just looked at Martys link, and the setup is pretty much identical with what we've got. But we paid a supplier to install it, so that's why we paid more.

Edited by onetrack
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Thanks for the comments guys, you may have saved me a bunch of work for little result.

Personally, my system cost a lot less than what I would hope to sell to strangers for, but I couldn't match a carbon filter setup for price.

 

There is something attractive about a solar-powered production system though that I like. Another example would be to produce hydrogen by electrolysis of water using solar and wind. This is way beyond the likes of me though. But suppose you could buy a system for a few thousand and run everything on the hydrogen it supplied, with no more input required. Dream huh?

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I like your idea Bruce. I recently put a three stage filter on the entry to the house. I shied away from the UV treatment which seemed to be unwarranted. I'm not worried too much about virus or bacterium. My decision to filter was mostly motivated by our thick layer of moss that insists upon building up in the guttering. I expect that the microorganisms dwelling in its wet little ecosystem are most likely digestible. But there might also be some not so nice ones. And a friend once got a bad dose of giardia from his tankwater.

 

 

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38 minutes ago, Bruce Tuncks said:

my system cost a lot less than what I would hope to sell to strangers for, but I couldn't match a carbon filter setup for price.

The benefit for you is that you figured out how to do it and did it for yourself. It works and you gained knowledge, experience and satisfaction from doing it. The bonus was that you saved a lot of money.

 

Over the past year I have made myself a sand blasting cabinet, a tumble cleaner, a spokeshave and other hand tools. At the moment I'm halfway through making a superhero helmet for my grandson. None of these things has cost me anywhere near a commercial price to make. In a world where you get more kicks in the arse than pats on the back, we must be satisfied with what we can do for ourselves, and not bemoan the fact what what we have done won't make us millioniares.

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I think I've related this story before - but it's worth repeating, just to show that it's amazing what the body can cope with. When the brother and I first started in agricultural earthmoving in '64-'65, we leased a vacant farmhouse from an early farmer client.

He'd bought out a neighbouring farm, and this nice roomy brick farmhouse (about 15 years old) was empty, and he wanted it occupied. So we leased it in exchange for the construction of a new farm dam each year. We lived there from 1965 to 1972.

The water supply for the house came from a 12,000 gallon (55,000 litre) ground level concrete tank, that was fed from the roof of a big shed. The tank was roofed and sealed, including the downpipe entry.

 

The water was pumped via a windmill from the ground level tank to a tank on a 4.5M high stand near the house to give us water pressure in the house. We lived there quite happily until the late 1960's, which is when we noticed these little dark flecks starting to appear in the water from the taps in the house, and in the bath.

 

We looked at them, couldn't figure out what they were, and shrugged it off. Then the flecks turned into black chunks a couple of months later. We got really curious by now, and decided we'd better have a look in the tanks.

The concrete tank was investigated first - and what we found, appalled us! The sealing arrangement around the downpipe entry to the tank had fallen off - and thirsty rats had been running down the downpipe (which ended well above the water level, even when the tank was nearly full - then jumping off the end of the downpipe to get a drink. Of course, they couldn't get out, and they drowned in there.

 

There must have been 100 decomposed rat carcasses in the tank! Some were still floating, some were totally decomposed, and had largely sunk - thus leading to the "chunky bits" appearing in water from the house taps, and in the bath!

We had been drinking rat soup, for God knows how long! Yet, strangely enough, neither the brother, nor myself, nor his wife, nor his 2 toddlers, had suffered any ill-effects from the polluted rain water!

 

I guess we must have had clean, disease-free rats! Maybe a 100 rat carcasses in 55,000 litres of water is an acceptable WHO pollutant standard?

We had to pump out the concrete water tank, drain the overhead tanks, flush out all the water lines and tanks, and truck in some fresh rainwater - and from then on, we made sure that downpipe was properly sealed, and regularly checked!

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Whenever  we get good rain I syphon the bottom of my tanks out. It provides feed for the adjacent lawn and garden and makes the bottom look so much better, but the taste is still the same. I have heard of a rat dieing in the gutter and causing health problems, but over 40 plus years I have never had any problem.

I think I would have had worse problems if I drank the town water.

My first visit to Gladstone was memorable for the residents were putting out plastic dustbins on the road side and Queensland Alumina were filling them up with de mineralised water, in the meantime the water out of the mains was so coloured that my friends little daughter screamed when she was put in the bath. Settled down quickly when she realsed the red colour wasn't harming her. There used to be a story that the Town Council would fly a flag when the town water was fit to drink. i never saw the flag.

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