July 2000

Dangers of Home Water Storage
By Kelly A. Reynolds, Ph.D.

Home water storage is a practice many believe is essential in the event of an emergency, when water supplies might be unavailable or tainted. We need only look to the stockpiling craze of last December fed by Y2K fears for an example. Unfortunately, stocking a safe backup water supply isn't as easy as filling containers and storing them on the shelf until needed. In fact, a number of waterborne outbreaks have been specifically linked to improper or unsanitary home water storage methods.

Why store water?
In many parts of the world, storage of drinking water is a routine occurrence, especially in homes lacking a connected source for potable water. Even in developed regions, the desire to store water for further treatment comes either from a lack of trust in municipal water supplies or the need for preparedness of a natural disaster or any other event that might compromise one's water supply. Regardless of the reason, drinking water collected from unsafe sources outside the home and held in household storage vessels are susceptible to contamination either at the source or during storage.

Several factors complicate the storage of water (see Table 1) and may compromise the quality of the water collected. Even if stored water supplies are properly collected in sterile containers and treated to remove any original populations of viruses and bacteria, the presence of disinfectant-resistant protozoan pathogens may still pose a problem. Filtration combined with disinfection or boiling for three minutes remains the most effective way to remove these hearty organisms.

Table 1. Potential routes of stored water contaminants

  • Contamination via hands while collecting
  • Contaminated collection vessels (re-used containers)
  • Bacterial regrowth (pathogen proliferation)
  • Potential presences of organisms resistant to disinfectants (Cryptosporidium)

Evidence of contamination
Studies of water storage practices in underdeveloped countries provide the best epidemiological evidence linking stored water to infectious disease transmission. Awareness of potential contamination sources and knowledge of the safeguards available can help maintain safe water storage practices in any region.

A 1979 evaluation of metropolitan Lagos, Nigeria3, indicated an 11.2 percent prevalence rate of Entamoeba histolytica, a pathogenic protozoa. Interestingly, the commonality was not associated with type of water supply but by storage of household supplies. Likewise, a study of an agricultural-based community in Zimbabwe4 showed that household stored water had a higher percentage of samples contaminated with E. coli than tap water used to fill the storage vessels.

Following a cholera epidemic with more than 533,000 documented cases and 4,700 deaths that began in Peru in January 1991, researchers found that contaminated water stored in the home was one of the greatest risk factors for the disease.5 Evaluation of stored water supplies showed progressive contamination during distribution and storage, where fecal coliform counts were highest in water from household storage containers and lowest in city well water.

A study highlighted in a 1995 article in the Journal of the American Medical Association (JAMA) described a two-component prevention strategy, which allows an individual to disinfect drinking water immediately after collection (point-of-use disinfection) and then to store the water in narrow-mouthed, closed vessels designed to prevent recontamination (safe storage).2 The study determined combination of new disinfectant generators and better storage vessel designs make home water storage a practical and inexpensive alternative. It further stated that a home treatment and storage approach empowers households and communities that lack potable water to protect themselves against a variety of waterborne pathogens. That, in turn, has the potential to decrease the incidence of waterborne diarrheal disease.

Recommended procedure
Although there are potential hazards related to storing water in the home, there are a number of recommended procedures to follow if the need arises (see Table 2). Maintaining good hygiene during storage into sterile collection vessels is probably the most effective means of reducing the chance of microbial infections. Narrow-mouthed vessels-less than 10 centimeters-are useful to discourage dipping utensils or hands into the water. If the water was non-potable initially, it may be chemically treated (i.e., chlorine or iodine) or boiled prior to bottling or drinking. Keep in mind, though, that routine chemical treatments may cause adverse health effects over time (i.e., cancer effects).

Table 2. Maximizing stored water quality

  • Use new or sterilized containers made of food-grade plastic
  • Wash hands prior to collection of water and avoid touching the mouth or inner lid of the storage vessel
  • Carefully fill the vessel with water from the highest quality source available
  • Boil or chemically treat (disinfect) potentially contaminated drinking water
  • Store containers in the coolest, darkest space possible
  • Consume or replace supplies about every six (6) months, or less

Food grade storage containers made of high-density polyethylene, i.e., common plastic milk containers, should be used to prevent leaching of toxic materials such as lead or vinyl chloride from ceramic and PVC containers, respectively. Storing filled containers in a cool, dark place will reduce growth of harmful microbes but not completely eliminate their proliferation. It's best to consume or replace stored water supplies frequently (about every 6 months).

As preparation for an emergency, it's advisable to store supplies for treating water, such as equipment for boiling or chlorine or iodine tablets (see Table 3). Crude methods of filtration by using common household supplies such as newspaper, filter paper, gauze and cotton cloth may also help reduce pathogen transmission. Research shows that this method, along with chlorine treatment can produce an emergency potable water source from snow or rain.1

Table 3. Procedures for emergency drinking water disinfection

  • Boiling—Vigorous boiling for three minutes will kill any waterborne pathogen
  • Chlorine treatment—Check label of common household bleach for instructions or add 10 drops of a one-percent bleach solution per quart of clear water. Double amount if water is cloudy. Mix and wait 30 minutes.*
  • Iodine treatment—Common household iodine (2 percent U.S.P.) may be added using 5 drops per quart of clear water or 10 drops per quart for cloudy water. Mix and wait at least 30 minutes.*

Commercial chlorine and iodine tablets are available also at drug, camping and sporting goods stores.

Using the highest level of purified water possible as the source for stored supplies is vital in maximizing the long-term quality of stored water. Municipal tap water is frequently monitored in the United States and is required to meet a certain level of standards set by the U.S. Environmental Protection Agency. Point-of-use treatment devices provide an additional means for quality control of untreated water supplies and further improvement of municipal water sources.

When these treatment benefits aren't available, an awareness of potential sources of contamination and knowledge of safeguards available enables safe maintenance of water storage in the home or any other situation.

1. Kozlicic, A., et al., "Improvised purification methods for obtaining individual drinking water supply under war and extreme shortage conditions," Prehospital Disaster Medicine, 9:S25-8, 1994.
2. Mintz, E.D., et al., "Safe water treatment and storage in the home: A practical new strategy to prevent waterborne disease," JAMA, 273:948-53, 1995.
3. Oyerinde, J.P., et al., "The epidemiology of Entamoeba histolytica in a Nigerian urban population," International Journal of Epidemiology, 8:55-9, 1979.
4. Simango, C., et al., "Bacterial contamination of food and household stored drinking water in a farmworker community in Zimbabwe," Central African Journal of Medicine, 38:143-9, 1992.
5. Swerdlow, D.L., et al., "Waterborne transmission of epidemic cholera in Trujillo, Peru: lessons for a continent at risk," Lancet, 340:28-33, 1992.

 Dr. Kelly A. Reynolds
About the author
Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on the development of rapid methods for detecting human pathogenic viruses in drinking water. She is also a member of the WC&P Technical Review Committee.