Safe Collection and Purification of Drinking Water

Boiling Water Purification

You may have seen a reality show or watched a video online where a person is demonstrating how to use water purification tablets or drops. The person dips their canteen in the river or pond and fills it. Then they add two tablets, or add a few drops to the canteen. The person mixed it well and then waited the prescribed time before drinking. They missed one critical step however.

The entire drink line is contaminated when you dip a drinking container into contaminated water.

You probably have ordered drinks at a restaurant, ice tea, soda or even a glass of beer. The server carries the drinks on their tray to the table and as they pick up the drink you notice their fingers are holding the glass at the drink line, the very place you will put your lips to take a sip. Their fingers are all over the rim of the glass, their unprotected fingers.

Your canteen also has a drink line, a place where your lips touch as you sip. The water inside the canteen is purified but the drink line is not sanitized unless you follow specific steps.

Ideally, you will have two containers, because one could be used for collection of the contaminated water. Once collected the contaminated water is then filtered into a clean container. This way you do not have to worry about the canteen threads and cap being contaminated.

You would need a filtering medium so you can filter the water into a clean container. Once the filtered water is inside a clean container then you add your tablets or drops.

Of course, nothing is ideal, so if you only have one container then dip it, add your drops or tablets and shake well. Once mixed, loosen the cap and act as if you are going to pour some of the water out. What you want to do is make sure the treated water flows around the cap and threads. This is to destroy contaminates lingering there. Then replace the cap and wait the prescribed time. Most tablets require an extended wait period after treatment so make sure you read carefully.

Once you have a camp established, you could sanitize all collection containers in boiling water. Boiling is always the preferred method of water purification. It is always prudent to filter water even if you plan to boil it. Filtering removes certain debris and waterborne cysts that in some cases, can withstand boiling water.

Bacteria, protozoa and viruses can be harbored inside the cysts and other debris and thus are not destroyed by the boiling process. Once inside your stomach, the acid present would dissolve the cysts/debris, which of course would then release anything inside in to your system. A one-minute roiling boil is adequate in most cases.

Protozoa – Cryptosporidium

Potential health effects are gastrointestinal illness, diarrhea, vomiting and cramps. Drinking water is contaminated by human and animal fecal waste.

Methods that may remove some or all of Cryptosporidium from drinking water are

  • Rolling boil for 1 minute, boiling is very effective in killing Cryptosporidium
  • Filtration is highly effective in removing Cryptosporidium but you must use an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter)
  • Disinfection with iodine or chlorine is not  considered an effective method for killing Cryptosporidium
  • Chlorine dioxide has a low to moderate effectiveness in killing Cryptosporidium, chlorine dioxide is usually sold as water purification tablets and they may advertise they are effective against cryptosporidium

The ideal method is when you combine filtration with disinfection. This method has a very high effective rate in removing and killing Cryptosporidium when used with chlorine dioxide.

Protozoa – Giardia intestinalis 

Also known as, Giardia lamblia and its health effects are gastrointestinal illness, diarrhea, vomiting and cramps. Drinking water is contaminated by human and animal fecal waste.

Methods that can remove Giardia

  • Rolling boil for 1 minute, this is very  effective in killing Giardia
  • Filtration has a high effectiveness in removing Giardia when using an absolute less than or equal to 1 micron filter (NSF Standard 53 or 58 rated “cyst reduction / removal” filter);
  • Disinfection with iodine or chlorine shows some effectiveness in killing Giardia
  • Chlorine dioxide water purification tablets are known to be effective in killing Giardia
  • Combination filtration and disinfection has a very high effectiveness in removing and killing Giardia 

Bacteria and Viruses

All of the above-described methods are effective in removing and destroying bacteria and viruses in drinking water. Once again, the ideal method is filtration and then purification.

Iodine is effective as well as chlorine dioxide in killing bacteria and viruses, but as noted above iodine is not effective in killing certain protozoa. You cannot mix iodine with any other chemical to purify water; it can only be one or the other.

Methods that may remove some or all of viruses and bacteria from drinking water are

  • Rolling boil for 1-minute minimum
  • Filtration is not effective in removing viruses in most cases, but is proven effective in removing bacteria
  • Disinfection with iodine or chlorine has a high effectiveness in killing viruses and bacteria
  • Disinfection with chlorine dioxide has a high effectiveness in killing viruses and bacteria

There is debate about filters and viruses. Viruses are typically smaller than 0.1 micron and thus are not removed by the standard filtration device you would have in your backpack. There are filters that claim to be able to filter out certain viruses and they might very well do so, but in a field environment how do you know the filter is still effective. The only way you may find out is by becoming sick.

Have backup methods/filters or use a combination of filtration and purification methods to ensure your water is safe to drink.

In the United States viruses are not a huge problem because most deadly viruses such as polio and a few others has been eradicated, or people have been vaccinated against them. However, this is not to say that you would not be exposed to any virus.

CDC. (n.d.). Retrieved 2014, from