G1494

Drinking Water Treatment:
Emergency Procedures

When home drinking water supplies are interrupted, emergency or short-term treatment may be required. This NebGuide covers finding alternative sources of drinking water and treating contaminated water.


Bruce I. Dvorak, Environmental Infrastructure Engineer
Sharon O. Skipton, Extension Water Quality Educator
Thomas W. Dorn, Extension Educator


Emergency or short-term treatment may be required when the drinking water supply to your home is interrupted due to natural disasters, accidents, or other causes. Short-term treatment methods may also be used by campers and hikers.

This NebGuide discusses situations when emergency or short-term treatment will be necessary and describes methods that can be used to treat limited amounts of water intended for human consumption.

Alternative Water Sources for Different Emergency Situations

There are numerous situations, due to either natural or human causes, that can temporarily interrupt a water supply.

Because water is the most important nutrient for the human body, having adequate, drinkable water available is critical. The amount needed is different for each person and depends on factors such as age, health, activity, and climate. It is important that drinking water not be rationed when water supplies run low. Drink the amount you need today and try to find additional sources for tomorrow.

Alternative water sources you can use in an emergency include a stored water supply that has been prepared ahead of time, bottled water, “hidden” sources within the home (e.g., ice, hot water tank), and outside water sources. If an interruption occurs in a private water supply, the nearest public water supply is also an alternative water source.

For information on preparing and storing an emergency water supply, see Drinking Water: Storing an Emergency Supply (G1536). In certain situations, such as a large scale disaster, bottled water availability may be limited. To learn more about using bottled water as a short-term water supply, see Drinking Water: Bottled or Tap? (G1448). The emergency procedure methods discussed in this publication are for temporary drinking water needs. Long-term treatment methods are discussed in other NebGuides in the Drinking Water series. All publications mentioned here, as well as many others, are available online at http://water.unl.edu/drinkingwater or from your local University of Nebraska–Lincoln Extension office.

Causes of Interruptions to Water Supplies

Most water supply interruptions can be categorized into one of four types:

1. Loss of water pressure can occur due to incidents such as damage to the water distribution system (e.g., water main break) or electrical failure. When this occurs, water is unavailable at the tap.

Alternative water sources may include:

Most Desirable

Less Desirable

Least Desirable

2. Known pathogen (disease-causing organism) contamination can occur after floods, earthquakes, or other natural disasters, or any time water is contaminated by human or animal waste. Pathogen contamination may be suspected in surface water sources such as lakes, ponds, and streams. Campers and hikers using surface water supplies should suspect human or animal impact and treat the water (see the “Emergency Treatment Principles and Processes” section).

Public water utilities occasionally issue “boil water advisories” when known pathogen contamination occurs. Emergency treatment should be continued until the boil advisory is lifted by the public water system. Guidelines for treating contaminated water by boiling, as well as by chemical disinfection, are discussed in the “Emergency Treatment Principles and Processes” section.

If bacterial contamination of a private well occurs, shock chlorination of the well and waterline is recommended (see NebGuide 1761, Drinking Water Treatment: Shock Chlorination). Treating water contaminated by a known pathogen is discussed in NebGuide 1826, Drinking Water: Bacteria.

Alternative water sources may include:

Most Desirable

Less Desirable

Least Desirable

3. Short-term accidental contamination of a private water supply with known chemical agents can occur from chemical spills during tank filling or back-siphoning during tank filling, or when any private well is contaminated from spills during chemical use.

Alternative water sources may include:

Most Desirable

Less Desirable

Least Desirable

4. Possible contamination with unknown chemical or biological agents may occur from intentional tampering with the water distribution system or source. In this situation the contaminant and when it was introduced are unknown. Emergency treatments described in this guide may or may not effectively treat the affected water source. An unaffected water source should be used.

The disinfection methods described in this publication will effectively treat water for most microorganisms commonly found in drinking water but may not necessarily remove certain biological agents, chemicals, heavy metals, or salts. It is important to seek professional guidance to determine what contaminants may be present in the water.

If you suspect intentional tampering with a public water system, contact your public water supply utility. If you are unable to contact the utility or if you suspect intentional tampering with a private water system, contact the Nebraska Department of Health and Human Services at (402) 471-2541.

In cases of contamination from unknown chemical or biological agents, temporary water sources include:

Most Desirable

Least Desirable

Hidden Sources of Water in the Home

If your drinking water supply is interrupted and you do not have an emergency stored water supply, you might turn to a number of water sources in your home.

In most situations, water from these sources should be treated by methods described later in this publication. If the interruption is due to power failure and only a short time has passed since interruption, water from the hot water tank or household pipes (described below) could be used without treatment. Water such as this in the plumbing is safe for only a few days and then must be treated before use. If there has been a major disaster, prevent contamination of the water in the house plumbing by shutting off the water valve that leads from the water main into the house.

Water Drained From Hot Water Tank

Some emergency water can be obtained from a hot water heater. If the water heater is old or the quality of the water in it is questionable (e.g., high sediment content), drain a few gallons of water every six months, allowing water to drain until it flows clean. This process will ensure that the tank and water remain free of mineral and rust deposits.

To obtain water from the hot water tank, follow these instructions:

Water Remaining in Pipes

You can drain the existing water in the pipes by gravity flow. Follow these instructions:

Water Dipped from the Flush Tank

Ice Makers or Other Appliances

Appliances such as ice makers in refrigerators may be another source of emergency drinking water.

If the ice was made before contamination occurred, it is an acceptable source of drinking water. Ice made from contaminated water should be melted and treated using a method appropriate for the contaminant. Emergency treatment procedures are described in the next section.

Outside Sources of Water

In certain situations water may obtained from outside sources such as swimming pools, ponds, or streams. Prior to consumption, outside sources will need to be treated using one of the emergency treatment procedures described in the next section.

Try to avoid choosing water from an area where human or animal waste may have contaminated the water. Also, try to obtain water from a clear water source. The nature of contaminants present in an outside water source is unknown, whereas contaminating agents in household waterlines are often known. Therefore, it is generally preferable to treat contaminated household water in a short-term situation and reserve treating outside sources as a last resort.

Emergency Treatment Principles and Processes

Inspect the water before treatment. Microorganisms may be attached to or embedded in soil or other organic particles suspended in the water. The water to be treated should be allowed to stand so the suspended material settles to the bottom of the container. Coarse materials like sand will settle more quickly than finer materials suspended in the water.

During and after settling, care should be taken not to agitate the water. Water from the top of the container can be gently poured or drawn off into a second clean container. A second option for removing suspended particles is to strain the water through a clean cloth, layers of paper towels, or a paper coffee filter. Do not use a commercially available portable water filter (see “Filtration”) for this step, as the suspended material may rapidly clog such filters.

For emergency or short-term situations, water can be treated using heat, chemical treatments, or filtration. Each method has certain advantages and disadvantages that must be considered. In some situations, a combination of these methods may be preferred (e.g., filtration and chemical treatment).

Contaminants in water which may cause illness or disease include bacteria such as E. coli, protozoan cysts such as giardia or cryptosporidium, and viruses such as Hepatitis A. Giardia or cryptosporidium are not likely to be present in Nebraska groundwaters but may be found in contaminated surface waters. Viruses should be suspected in any water that may be contaminated with human waste.

Heat Treatment

Heat kills microorganisms and is the oldest effective means of disinfecting drinking water. Adequate heat treatment will kill virtually any disease-causing organism, including bacteria, cysts such as giardia and cryptosporidium, and viruses.

Heat the water to a vigorous boil for one minute, which includes an adequate safety factor. Any longer could concentrate other chemical contaminants that may be present. Since water boils at a lower temperature as elevation increases, the Centers for Disease Control and Prevention (CDC) recommends boiling for three minutes at altitudes above 6,562 feet (2,000 meters).

Though boiling effectively disinfects water for drinking, it does not provide a residual (or long-term) disinfection; therefore, care must be taken not to recontaminate the water.

Boiled water may taste flat. The taste can be improved by pouring it back and forth between two clean containers to reoxygenate it or by adding a pinch of salt to each quart after it has cooled.

Chemical Treatments

Chlorine and iodine are the most commonly used chemicals for emergency disinfection of water.

The killing effectiveness of the chemical depends on the concentration of the chemical in the water, the amount of time the available chemical is in contact with the water prior to use (contact time), the water temperature, and the characteristics of the water supply.

A decreased concentration of the disinfectant or a lower temperature will require a longer contact time for adequate disinfection. If the water temperature is less than 41°F (or 5°C), it should be allowed to warm prior to disinfection or the chemical dose should be doubled. If the water is cloudy, strain it through a clean cloth, layers of paper towels, or a coffee filter before treatment.

A common objection to chemical disinfection is the flavor it gives to the treated water. If flavorings of any kind are added to the water to improve taste, it should be done after the recommended contact time for disinfection. Flavorings added before adequate contact time has been achieved will “tie up” some of the chemical available for disinfection. Adding about 50 mg of vitamin C (ascorbic acid) per liter or quart of water after the contact time can improve the taste. Vitamin C is often available in 250 and 500 mg tablets where vitamin supplements are sold. Tablets should be pulverized and divided before adding to the water. In addition, freshness preservatives containing vitamin C are often available where canning supplies are sold.

Bacteria are very sensitive to chemical disinfectants such as chlorine and iodine. Viruses, cryptosporidium, and giardia require very high dosages of disinfectant or longer contact times with the disinfectant than the standard recommendations. Heat treatment is recommended if these pathogens are suspected in the water.

Chlorine. Regular household chlorine bleach that contains 4-6 percent sodium hypochlorite as the only active ingredient can be used for disinfection. Bleaches with labels such as “Fresh Wildflowers,” “Rain Clean,” “Advantage,” or labeled as scented may contain fragrances, soaps, surfactants, or other additives and should be avoided for drinking water disinfection.

For clear water, add six drops per gallon with a medicine dropper. For cloudy water, strain water through a clean cloth, layers of paper towels, or a coffee filter prior to treatment and add a larger disinfectant dose of 16 drops per gallon. Stir the water and let it stand covered for 30 minutes. For adequate disinfection, the water should have a slight chlorine odor to it after the 30 minute waiting period. If this odor is not present after the 30 minutes, repeat the dose and let it stand covered for another 15 minutes. If this odor is not present, the bleach may have lost its effectiveness due to age or exposure to light or heat.

Use the freshest chlorine bleach available. If the chlorine taste is too strong in the treated water, taste can be improved by pouring the water from one clean container to another several times.

Halazoner® tablets are another form of chlorine for drinking water disinfection. The tablets are convenient and inexpensive but may require high doses and longer contact times. Follow manufacturer directions for use. Chemical treatment with chlorine provides some protection against recontamination since some available chemical remains in the water.

Iodine. Two forms of iodine commonly sold for chemical disinfection of drinking water are tincture of iodine (2 percent) and tetraglycine hydroperiodide tablets (Globaline®, Coghlan’s®, and Potable-Aqua® are examples).

Iodine was once widely used, but is no longer recommended because health research has shown that as many as 8 percent of people have hidden or chronic thyroid, liver, or kidney disease which iodine can make worse. Iodine should not be ingested by children younger than age 14. Do not use iodine-containing products unless you have discussed the risks with your physician.

Filtration. Commercially available portable filters provide widely varying degrees of protection against disease-causing contaminants. The better filters provide adequate protection but less sophisticated filters (often less expensive) may not provide protection.

The more sophisticated filters typically operate by a hand pump which draws water into the filter through an intake hose or by slow gravity flow through a filter or series of filters. The filtration process works by physically removing the contaminants from the water and retaining them within the filter medium. The size of the contaminants retained depends on the pore size or the space between media fibers or granules. Most filters list an average pore size and are rated by the manufacturer according to the smallest particle they can trap.

For example, a one micron (one thousandth of a millimeter) filter traps contaminants one micron in diameter or larger. The removal percentage of contaminants is affected by the amount of time the water is in contact with the filter media. Shorter contact time generally results in less contaminant removal. Some filters have a chemical treatment component such as activated carbon or iodine-impregnated resins which are effective against bacteria and some viruses. The contact time with the iodine in the filter may be too short to kill protozoan cysts, however.

Portable filters do provide immediate access to drinking water without adding unpleasant tastes or odors. However, as with boiling, the water can become recontaminated after filtration. Also, portable filters sold for field use with pore sizes of 0.1 to 0.3 microns may be acceptable for cysts and bacteria but do not have small enough pore sizes to reliably remove viruses. While the filters may be reliable in remote areas where human waste contamination is unlikely, in populated areas filtration should be followed by either chemical disinfection with chlorine or boiling as described previously.

Proper selection, operation, care, and maintenance of portable water filters is essential for producing safe drinking water in emergency or short-term situations. When considering the purchase of a filter, be aware of the filter’s rating for pore size, output, pump strokes per liter, and pump force (how much effort is required to operate the pump). If size and speed are not critical factors, a gravity-fed drip filter that lets water slowly drip from a reservoir down through the filter may be a good option. Be aware that membranes in some filters can be damaged by chlorine in the water. Also, cloudy or turbid water can quickly clog a filter and shorten the life of the unit. When using a portable water filter, always follow the manufacturer’s instructions for use, care, and replacement.

Summary

Emergency or short-term treatment of drinking water may be necessary due to natural disasters, accidents or other situations caused by humans. Alternative drinking water sources for emergency situations and short-term use may include a stored emergency water supply that has been prepared ahead of time, bottled water, hidden sources of water within the home, and outside water sources. When a stored water supply or bottled water supply are unavailable, alternative water sources may be made acceptable for drinking by use of heat, chemical disinfection, filtration, or an appropriate combination of these methods. Each method has advantages and disadvantages, which should be considered for individual situations.

If local public health department (or water utility) information differs from the recommendations in this publication, the local information should be followed. Local officials will be familiar with site- and event-specific conditions.

Acknowledgment

The authors wish to acknowledge the contribution of former UNL extension engineer Jodi Kocher, who collaborated with them on the previous version of this NebGuide.

This publication has been peer reviewed.

Disclaimer

Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by University of Nebraska–Lincoln Extension is implied for those mentioned.


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2004, Revised May 2009

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