Positive coliform tests - will chlorinating help?

You should do some basic research before coming here.

chlorine as disinfectant for water

Much more needs to be know about the water supply before any problem should be addressed. If you talking about household domestic drinking water, a thorough general "Potability Test" panel should be done, including VOC's. Then we need to know someting about the source of the water, the facility it serves, and a bit about the tanks themselves Ie; what kind and how big are they (how many) etc. Is your water pressure generated in-house, etc. Is it E. Coli or total coliform that is present here and how often do you test for it, how long have you known?? Is this a recurring or first time problem?

Chorination is generally a good idea but more info would help determine what strength and for how long it should stand in the system.

To solve the problem, you need to figure out how e.coli is getting into the tanks, and prevent that from happening. What is the water source in your system? Where are the tanks situated? How are coliforms coming in contact?

Using chlorine to disinfect tanks is feasible - I mean to clean the tanks before using the system, once you have addressed the cause of the contamination. A strong chlorine solution would be recommended for that purpose, then rinse out and refill.

For water consumption in the meantime, you should boil the water before use. Boiling is a reliable way to kill coliforms.

<...Boiling is a reliable way to kill coliforms....>

Prior to consumption, quite.

Once the source of the coliform contamination is identified and corrective measures implemented, one should give consideration to ozone sterilization as an alternative to chlorine.

Is your water tank located near your septic tank? If so, you've got a far worse problem than just E. coli in your water. It would mean that your water tank is contaminated with sewage. If your water tank is in a water tower or on your roof, then it would likely mean that your tank cover is punctured and that animal droppings are getting into your water. Better identify and rectify this problem first before doing anything else.

Thank you all for the good ideas, The tanks are on a tower and my worry is that the mains feeds both the tanks and the outlet(taps). That is the taps are supplied from the tank (in case of the mains is not flowing) and directly from the mains supply. So I am not exaclty sure whether the contamination is from the tank or the mains supply.

All the same I will retake a sample from the mains supply and the Tank and do testing again. Hope that will help me know the source of contamination.

It's a good idea to compare samples from the mains supply and the tank.

When you take a water sample from taps, don't forget to disinfect them first, and run the water for a minute or so before taking your sample, to avoid any false readings because of contamination in the taps area.

Good luck.

You might want to boil the drinking water or install a UV light if it is a permanent situation. Chlorine is easy for a quick flush but is not exactly good for your health. Make sure you don't overdose.

You should inform the authorities about this as other people might be affected.

Good luck.

Please consult with the AWWA specifications for the disinfection of water storage tanks. Offhand I cannot remember which section, but I'm steering you that way.

Also, many State Health Departments in the USA set stricter disinfection standards then AWWA. You didn't state where you're from....only assuming for now that you're in the USA.

Have a great sunny day!

Some quicky question regarding your water storage tank and the supply, okay?

What is the source of your water? Pumped well(s) or surface water such as a river or lake? If a well source, is it adequately capped? Are there many farm animals or wild animals defecating in the vicinity of the wellhead? Well depth? Has the well ever been disinfected?

Does the water storage tank have a completely sealed roof, or is it completely open to the elements and birds?

Is the water distribution system disinfected with chlorine presently? Typical Chlorine residuals, if any, at faucets and dead ends of pipe lines? Given that you're in Africa and tropical weather, I strongly suggest that you disinfect your water supply continuously with injection point located in the water supply main some place very close to the well head and furthest away from the tank so as to achieve adequate microbial disinfection and chlorine contact times. You can inject into the main conveying the raw water with liquid Sodium Hypochlorite solution (same stuff used for disinfecting swimming pool water....HTH......even chlorine bleach will work and is fairly inexpensive!) using inexpensive chemical metering pumps (should have a pair of them...one for backup in case of a pump failure)...the metering pump can be paced directly to the actual well output rate using specialized flow meter that produces electrical pulses that in turn drive the chemical metering pumps. By disinfecting your water supply you can eliminate many water borne diseases that occur constantly around the world in poorer nations such as yours.

Good luck finding the source of the contamination, and please, have a great sunny day!

< www.ontario.ca/drinking water/stel01_046942.pdf >

The above site is a connect with Ontario Ministry of Environment and is based on AWWA manuals and recommendations.

Hello Luyomba:

Sorry for the Guest tirade. I will also recommend he be banned.

I hope you have easy access to chlorine and testing of chlorine residuals in Rawanda. This web site should give some insight in chlorination of storage, mains, and contact and residuals required at various contact times and pH. A method of thinking of CT values is to think of Chlorine residual required and Time of contact, hence the CT. If you don't have equipment to measure, a 50 mg/L dosage in a reservoir can be achieved by adding 1 liter of 6% bleach for every 1200 Liters of water in storage or 1 liter of 12% bleach dissolved in every 2400 Liters in storage. I would double this dosage if the water temperature is high and you need the 24 hours of contact with the solution. The residual will diminish with time. Following the disinfection time you will have to flush and resample the water. I suggest three consecutive negative results before you consider all may be safe.

It is also suggested that if you have a well, you follow a similar procedure within the well and of course the mains. You will have to assure you wash down all walls in the storage tank and that the contact can reach either the 24 hours or that calculated from the web site provided.

Others have suggested further testing and protection of the source, I would agree. We only know that which you can provide. It sounds like some sort of continuous treatment barrier may be required.

Good Luck

50mg/litre... Isn't it equal to 50ppm (parts per million)?

What I understand is 5ppm or even as low as 0.5ppm at point of use is enough to make water safe for drinking?

Please clarify..

Sisra:

Yes for all practical purposes 1 mg/L is the same as 1 ppm. It is much easier to think of mg/L when doing computations and mg/L is the standard used internationally. For example 6% chlorine is 60,000 mg of chlorine in each Liter of chlorine solution. If 50 mg/L is the dosage required then simply divide the 60000 mg in each liter by 50 to get the number of liters in storage disinfected with each liter of 6% chlorine solution used. (answer is 1200 liters of storage disinfected). Care must be taken to disinfect all parts of the storage tank in question.

The American Water Works ass, <www.awwa.org> has a bookstore that will lead to the standards of operation. Included you will find standards for disinfecting storage tanks and mains. Unfortunately these standards are sold to most operators of water treatment plants and cost about $50.00 each.

50 mg/L is the dosage required to disinfect mains that are new or under repair. Storage is a bit more complicated but usually 50 mg/L is ok if 24 hours of contact is acquired at that level of disinfection.

Normal disinfection requires CT values of usually 10 to 20 or another way of saying this is to have dosages of 1 mg/L with a 10 minute contact time or any combination of Chlorine residuals multiplied by minutes of time that will equal 10. A CT of 20 is used in some cases. Under there normal conditions you will be getting good disinfection with low resduals and good contact times. However when disinfecting storage or mains under repair or when some adverse condition has arisen, I would suggest something higher than normal and the AWWA standard is a good starting point. Do not confuse point of use disinfection with emergency or new disinfection. I was assuming that this is the type of disinfection that was required.

0.5ppm is added to mains-distributed water in the UK, so as to protect the water while it is in the piping system. Increasing the dose rate above, oh, say, 2ppm will make the water undrinkable on the basis of palatability and taste.

There are water supply regulations in the UK that apply to the distribution of mains potable water within buildings. Water intended for consumption will not usually be stored in tanks. Some private supplies will need to be stored in tanks, and these are probably best protected by a combination of fine depth filtration and ultraviolet sterilisation immediately prior to use; each installation is best considered on its merits.

I am thinking of Chlorinating the water tanks, could someone advice if this will solve the problem, and what could be the possible ratio of the chlorine and water.

But because you can doesn't mean you should use chlorination, often ultraviolet light or ozone use is preferable health wise.

Get the appropriate testing results and determine the source before the method remedial action is decided.

Over chlorination will only be successful short term if there is sediment in the holding tank. Penetration into the layer will be not more than 10mm. Below that, the bacteria will still multiply and give rise to sudden bursts of failures as the gasses build up and then escape.