Select Page

Image via Pexels


What do you do when your facility water test comes back positive for coliform? Well, there are different methods of disinfection that you may decide to use at your business premises. Read on to learn more.

IMPORTANT NOTE: This article is designed to provide you with advice only. Coliform is a potentially dangerous bacteria, and you need to make sure your water supply is free from infection. Speak to your local environmental agency if you are uncertain about any aspect of treating your water.

Boiling the Water

Boiling is one of the most straightforward and effective responses when your water test came back positive for coliform. This is a familiar method of dealing with bacteria in water – and for good reason. High temperatures destroy bacteria such as coliform so it cannot cause a public health danger.

Generally, increasing the temperature of water or another substance to between 145 and 165 degrees Fahrenheit will destroy most types of bacteria. To be on the safe side, raising the temperature to boiling point ensures there is no ambiguity or uncertainty, and the bacteria is safely denatured and neutralized.

There is a problem here, though. Boiling water in this way is only a feasible option at very small volumes. It may be impractical to boil large amounts of water within your systems. So if there is a coliform infection in your water supply, the boiling method may only be suitable for purifying small amounts of water for specific uses.

Chlorine Bleach

Adding a disinfecting agent to the water supply may be a more feasible option for businesses who need to remove coliform bacteria on a broad scale. This option is far cheaper and easier to achieve than large-scale boiling. But how effective is it?

In many cases, coliform outbreaks occur after a one-off event, such as a heavy rainstorm or the installation of new equipment in the water storage system. This can often be counteracted with a one-off application of chlorine in high concentration. This process is known as shock chlorination, and it is intended to remove the infection with maximum efficiency.

The advantage of shock chlorination is that it does not require you to expose the water to chlorine in the long term. Excess chlorine can remain in the water and cause toxicity issues, which then need to be dealt with. However, a study from Penn State found that around 15 percent of coliform-infected wells treated with shock chlorination and sealed with a sanitary cap were successfully disinfected. This means that the infection is likely to linger in the vast majority of cases.

In these cases, additional doses of chlorine may need to be added on a continuous basis to rid the well of infection and to keep the water free from coliform. Steps will need to be taken to remove the chlorine before the water can be used.

UV Light

Ultraviolet, or UV, light is another method that can be deployed to remove bacteria in the event that a water test comes back positive for coliform. There is no need to add any potentially harmful chemicals, and the UV light does not leave any residual trace in the water. The high-frequency radiation simply kills the bacteria, leaving the water safe.

A UV light bulb is placed within the water supply, protected by a sleeve made from quartz glass. Water flows over this glass sleeve and is exposed to the ultraviolet radiation. This method has been shown to be successful in water supplies where the infection rate is less than 1,000 colonies of bacteria per 100 mL of water – or 100 colonies per 100 mL in the case of a fecal coliform infection in the water.

However, there are a few things business owners need to make sure of if they do decide to utilize this method.

  • First, the water itself must be clear. If this clarity is occluded by sediment or by high levels of turbidity, this may prevent the UV radiation from reaching the bacteria, and the method may not be successful.
  • Second, the glass sleeve needs to be kept clean and free from any contamination that may hinder the bulb’s effectiveness. Buildup of sediment on the glass – something that will happen over time – will block the UV radiation and reduce its efficacy.

You will need to decide if the coliform level is low enough to deploy this method, as well as how you will keep the water and the glass sleeve clear so the UV can do its work.


Adding ozone, or O3, to the infected water is one method of removing the coliform bacteria. Ozone works in a similar way to chlorine, oxidizing and killing the bacteria in the water sample. However, utilizing ozone is a little more difficult than deploying chlorine.

This is because, while chlorine can be transported and stored, ozone is far more unstable. As such, it must be produced onsite, ready for use in disinfecting the water. Ozone is produced using electricity at a high level of energy and then deployed as an oxidant agent in the water supply.

This is an expensive process and one that might not be feasible for all businesses, although there are some use cases in which ozone is the preferred option. If you need to disinfect your water while also removing iron and manganese, ozone might be the best choice.


Iodine was once the go-to agent for disinfecting water at scale. However, the U.S. Environmental Protection Agency (EPA) has voiced concerns about the safety of iodine and the dangers of long-term exposure to the element. As such, they recommend iodine only for short-term use or for situations in which emergency disinfection is needed.

If you have done any hiking or mountaineering, you may already be aware of iodine tablets that are used to purify water ready for drinking. Industrial applications of iodine work in much the same way – just on a larger scale. We have included iodine here simply to let you know which options are at your disposal. But it is unlikely that the chemical will be suitable for the needs of your facility.

What to Do if Your Water Test Came Back Positive for Coliform

You need to be ready to deal with the problem if you have a positive test for coliform. Research the different disinfection methods and make sure the one you choose is suitable for your purposes.