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There is an 8000 liter water tank on top of my house which provides water for the house.

Bacteria, fungi, algae, etc. often start developing in the tank, giving unpleasant smells, etc.

The water is ground water that we pump up there with our own pump.

The tank is made of concrete and covered with a steel lid.

Nobody is drinking or cooking with the water. It's used for stuff like laundry, showers, washing dishes, etc.

What can I do to prevent these unpleasant qualities of the water? It's very hot here (like 40 celsius in the shade), and the water tank is in the baking sun.

My landlord is unlikely to want to make any large investments. Therefore, cheap solutions are a plus.

Edit: Several answers have suggested chlorination, and it seems like the best option. But I live in rural India and it's difficult to find chlorine here. Bleach, though is readily available. Does it seem suitable? I've asked this as a separate question on Chemistry SE.

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Fiksdal
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    The conventional solution is to treat the water with chlorine additive. – Michael Karas Jun 02 '16 at 19:15
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    Also helpful would be filtering and a UV bulb, but chlorine would still be the answer. The real issue is nitrogen from the rainwater provides nutrient for stuff to grow. – Ben Welborn Jun 02 '16 at 20:14
  • Oh! I made a slight mistake, I was thinking that it was a cistern... but if you have bacteria or other stuff growing in it, then still yes, nitrogen (microbial food) is why. Water that does not have any nutrients cannot support microbial growth. Normally, the ground does filter out nitrogen. Speculatively, nitrogen may be comming from farm runoff, or sewage, or maybe rain water is getting into the ground water too quickly to be filtered out. I'm sure that if you get it tested for nitrogen, you will see that it's high. – Ben Welborn Jun 02 '16 at 20:32
  • A carbon filter will help reduce nitrogen... chlorine will react with nitrogen. – Ben Welborn Jun 02 '16 at 20:37
  • I will give you a hint: snark in the face of free advice is not likely to get you any further advice. – bobfandango Jun 05 '16 at 05:04
  • @bobfandango This was *honestly* not meant as a snark!! Or even sarcasm in any way! I was just trying to be witty (rather unsuccessfully, it appears) – Fiksdal Jun 05 '16 at 05:06
  • @BenWelborn Someone pointed out that one of my previous comments to you might be interpreted as a snark. I really hope you didn't feel that way. Just wanna say that I totally didn't mean it that way, it was meant as a friendly joke. If it came across wrongly, I'm very sorry. Not my intention at all. – Fiksdal Jun 05 '16 at 05:08
  • @bobfandango The part about the septic tanks is true, by the way, that is actually the situation here. – Fiksdal Jun 05 '16 at 05:37
  • It was a little bit of a faux pas; and I was kind of wondering if my mentioning sewage was taken as an insult (it was not meant to be offensive). The fact is, sewage in the ground water is horrifying, but unfortunately it happens. SO, I'm not sure what the situation with the septic is, but trust me when I say that there is food for the bacteria in the water and chlorination (calcium hypochlorite tablets) is the cheap and guaranteed solution. – Ben Welborn Jun 06 '16 at 12:52
  • @BenWelborn It was definitely not taken as offensive, and I had no intention of sarcasm either. I was just trying to be funny, unsuccessfully, it appears. And yes, septic tanks draining into the ground is a huge health hazard here. My drinking water goes through RO, UV and ozonization. Thanks for the chlorine tip. It will probably be the solution. Good answer. – Fiksdal Jun 06 '16 at 13:09
  • @bobfandango Did you think I was joking regarding the septic thing, btw? Why did you think it was a snark? I'm honestly asking because I want to avoid such misunderstandings in the future. – Fiksdal Jun 06 '16 at 13:57
  • Hey, if no snark intended, then my bad. Apologies. It was the combination of replies that makes it seem bad to me. Saying, "Interesting" when rain water clearly is not a factor just seems sarcastic. Then "I will give you a hint" also sounds the same way. But I see from your profile now that I look that english is not your first language, so I jumped the gun there. Again, apologies. – bobfandango Jun 07 '16 at 00:13
  • @bobfandango No problem, just glad to have cleared it up :) – Fiksdal Jun 07 '16 at 05:31
  • Actually, this reminds me of a time in Mexico where I was trying to speak Spanish with a guy. Of course, my Spanish is horrible and he switched to English. I said, okay, thanks, sorry about the Spanish, but thought I'd try. He replied simply, "Nice try." In the States, "Nice try" is frequently a sarcastic reply... depends on tone of course, but often it is. Anyhow, of course he didn't mean it that way, and I'm sure had no idea it is sometimes used/construed that way. But my wife and I laugh about it to this day.... – bobfandango Jun 07 '16 at 17:07
  • @bobfandango LOL.. Yeah that's good. "Nice try" often implies that you think someone's lying or cheating. lol. Like in Danish they say "Hold kæft" (literally "shut your mouth") to indicate that someone said something interesting. I always have to remember to not get offended when I talk to Danish friend and they say that :) – Fiksdal Jun 07 '16 at 17:17

4 Answers4

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Besides the suggestions above some things you might try:

Oxygenation: a small pump set up in the tank pumping the water into the air gap above water float level you have or an air pump pumping air into the water might help with some of the issues. The pump can be placed on a timer to cut down the electrical expense.

Refreshing the water on a regular basis. A tank I set up for a Solar off-the-grid type situation pumped continuously into the tank during the day, (but with solar powered pump, so pumping was free), and the tank had an overflow outlet near the top which could be tapped into drip irrigation system. Water was exchanged continuously, keeping growth down. An alternative to this would be flushing and refilling the tank on a regular maintenance schedule.

Lastly, and possibly the best solution, would be simply placing a filter canister with a taste/odor filter cartridge between your tank and rest of the home.

user2448131
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You should treat it like a (small) swimming pool. Maintain the free available chlorine (FAC) level between 1 - 3 parts per million (PPM). PPM is basically the same as milligrams per liter. So for 8000 liters you need 8 - 24 grams of chlorine. I would use calcium hypochorite powder/granules, which is commonly 65% Ca(ClO)2 by weight; so you will need 12.3 - 36.9 grams to treat your tank (see video about adding Ca(ClO)2 to pools).

Of course this is a little over simplified. You will need to add chlorine after you add water and as chlorine evaporates. Monitoring chlorine levels and keeping everything balanced takes some extra equipment and it's too lengthy to write all of it up here, but you should have a pool pump and filter and a pool chemistry test kit (see video for info about the kit). This may seem daunting, but I believe that this tank will be easier to maintain than an actual swimming pool because you will be using/replacing the water, so you will get familiar with adding chlorine once in a while or as you fill the tank.

Regarding a pool pump, I don't think that you need something heavy duty... for example, a cheap and easy pool pump like this (Intex Cartridge Filter Pump) should work fine:

enter image description here

You should probably make a shelter or use a dog-house if you decide to get this (particularly cheap) pump; keeping it from being exposed to weather will make it last much longer. Also, setting it on a timer (like 4 hours per day) would probably be enough to keep the water circulated and again, extend the life of the pump. And be sure to keep an eye on the filter; I'm not sure how often it will need to be changed, but I would guess (probably) twice a year.

Ben Welborn
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  • Thanks. I guess I'll experiment with different chlorine levels to see what works. BTW, what exactly does the pump do? – Fiksdal Jun 07 '16 at 16:54
  • I live in rural India and it's difficult to find chlorine here. But this product is available. Would it be suitable? https://www.thecloroxcompany.com/products/ingredients-inside/en-us/clorox/cloroxregularbleach1concentrated/ – Fiksdal Jun 07 '16 at 17:08
  • @Fiksdal The pump circulates the water (which helps mix the chlorine) and it has a filter to catch any buildup. You don't really need to experiment with chlorine levels. I would add ~37 grams of 65% Ca(ClO)2 to the full 8000 gallon tank. Then keep it maintained at 1 - 2 ppm... which means you need to check it occasionally with a kit. PPM = mg per liter. If you need to add 1 ppm then you add 12.3g of 65% Ca(ClO)2 (into 8000 liters). – Ben Welborn Jun 07 '16 at 17:17
  • I see. The pump sounds useful, as dead bugs often accumulate and decompose in the tank. Did you see my other comment? I don't have access to these exact chemicals. Any thoughts on the product I linked to? – Fiksdal Jun 07 '16 at 17:19
  • @Fiksdal regular chlorox is 5% or 6% NaOCl. So the amount you need to add would be about 160 ml per each ppm. – Ben Welborn Jun 07 '16 at 17:20
  • Nice. There's nothing else in Chlorox that would make it unsuitable for use? – Fiksdal Jun 07 '16 at 17:23
  • I've asked it as a sepreate question here: http://chemistry.stackexchange.com/questions/53341/are-these-chemicals-suitable-for-disinfecting-my-water-tank – Fiksdal Jun 07 '16 at 17:40
  • @Fiksdal It has other ingredients, but chlorine is the most important. I would not drink or cook with water with 1ppm chlorine, but it should be ok for laundry and showers. – Ben Welborn Jun 07 '16 at 17:48
  • Cool! This is great. – Fiksdal Jun 07 '16 at 17:52
  • @Fiksdal I went ahead and answered [your 2nd chemistry question](http://chemistry.stackexchange.com/questions/53341/are-these-chemicals-suitable-for-disinfecting-my-water-tank/53531#53531) since they couldn't (or wouldn't). – Ben Welborn Jun 10 '16 at 22:53
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Since this is for a "not for drinking", unfiltered, untreated, non-potable water storage tank. It seems your goal is just to reduce the levels of bacteria/fungi/algae in the water.

If you can get the interior water temperature over 50 deg C, you start killing off the stuff living in the water. With 40 deg C in the shade, it sounds like you have lots of free solar energy to heat the storage tank with, something like a thermosiphon could work.

Another thing that should help is putting a large coil of bare copper wire in the water, when the large surface area of copper slowly starts corroding, it will flood the water with copper ions known to kill off bacteria and algae.

Netduke
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  • There are many (common) organisms that grow at 50 - 60 °C. Bacillus subtilis comes to mind. 60 °C will kill non-spore formers, but the amount of time depends on how much bacteria was present to begin with. Most spore forming bacteria will survive for days at 70-80 °C. I wouldn't trust water held at 90 °C for two weeks to be free from bacteria (with or without copper). Boiling for 30 minutes is fine for a pot of relatively clean water, large amounts of water (180 liters) need to be boiled for days, depending on the bacterial load. For 8000 liters, boiling would be impractical and insufficient. – Ben Welborn Jun 02 '16 at 20:10
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Even though you are not drinking this water, you are using it for showers and for washing dishes - so it probably needs to be treated nearly as seriously as drinking water.

The main methods are filtration, treatment with floculants, thermal treatment and chlorination.

Chlorination is a widely used method. Chlorine is present in most disinfected drinking-water at concentrations of 0.2–1 mg/litre

The World Health Organisation (WHO) publish "A toolkit for monitoring and evaluating household water treatment and safe storage programmes" (HWTS):

Several HWTS methods have been proven to significantly improve drinking-water quality in the laboratory and in field trials in developing countries . These HWTS methods include filtration, chemical disinfection, disinfection with heat (boiling, pasteurization) and flocculants/ disinfectants. In addition, a combination of these methods may be used to increase the efficacy of treatment.

...

enter image description here enter image description here

Note that WHO cite "low cost" as an advantage of chlorination.

RedGrittyBrick
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  • Thanks. I agree that chlorination seems like the best option here. – Fiksdal Jun 07 '16 at 16:51
  • I live in rural India and it's difficult to find chlorine here. But this product is available. Would it be suitable? https://www.thecloroxcompany.com/products/ingredients-inside/en-us/clorox/cloroxregularbleach1concentrated/ – Fiksdal Jun 07 '16 at 17:08
  • I've asked it as a sepreate question here: http://chemistry.stackexchange.com/questions/53341/are-these-chemicals-suitable-for-disinfecting-my-water-tank – Fiksdal Jun 07 '16 at 17:41