Boiling vs. Filtration: Which Choice Is Safer?
By: Shin Jie Yong
Tags: Health, Advice, Education, Life, Science

Microbes | Lifestyle

Boiling vs. Filtration: Which Choice Is Safer?

Filtration only reduces microbial load and can’t eliminate viruses. But boiling does the trick.

Image by infopaul70 from Pixabay

“Microorganisms with a small infectious dose — Giardia, Cryptosporidium, and Shigella species; hepatitis A; enteric viruses; and enterohemorrhagic Escherichia coli — may cause illnesses even when a small volume of contaminated water is inadvertently swallowed…,” says Charles D. Ericsson, MD and infectious disease specialist in Houston, and colleagues in the journal of Clinical Infectious Diseases.

“Because total immunity does not develop for most enteric pathogens, reinfection may occur,” explains Ericsson et al. Most enteric pathogens can also survive in cold/frozen water for months. “Estimations of water safety cannot reliably be made on the basis of the look, smell, and taste of water,” they added.

Nearly 2 billion people in low- and middle-income countries do not have proper sources of “microbiologically safe drinking water.” This causes an estimated 500,000 deaths — mostly children — annually. International or wilderness travellers should also be aware of the microbiologic safety of drinking water.

Filtered vs. Boiled

“Yes, it is important to boil all tap water even if it has been filtered. Most water filters (activated carbon, charcoal, pitcher filters, etc.) are not suitable for use on microbiologically unsafe water and do not kill bacteria or viruses,” explains John Woodard, a water specialist at Fresh Water Systems Inc.

The Centers for Disease Control and Prevention (CDC) also states that “filtration is not effective in removing viruses,” but boiling water for just one minute does the trick.

Filtration lowers pathogen load whereas boiling kills all waterborne pathogens (Cryptosporidium, Giardia, Campylobacter, Salmonella, Shigella, E. coli, enterovirus, hepatitis A, norovirus, rotavirus), CDC says.

Magic of Boiled Water

Boiling water is a ‘golden rule’ followed by communities in rural areas of countries like China, Mongolia, Indonesia, Malaysia, etc. They have fewer diarrheal victims from contaminated water as a result, according to a 2017 meta-analysis of 27 studies. “Boiling has a strong and highly significant protective effect for nonspecific diarrheal disease outcomes,” write the authors from the Division of Epidemiology, School of Public Health, University of California.

Even in cities, the boil order — or boil water advisory — is launched in times of natural disasters, pipe leakages or chemical spills where chances are that drinking water is contaminated by waterborne pathogens. In such times, citizens are advised to drink only bottled or boiled (at least 1 min) water.

Why? Studies have concluded that 70°C exposure for one minute is sufficient to kill 99.999% of waterborne microbes, says the World Health Organization. The magic of boiling lies in the fact that protein — an essential component to life, even viruses — denature at high temperatures.

Note that some microbes still survive the boiling process but, fortunately, they don’t cause diseases when ingested. The Clostridium spores, for example, are ubiquitous in nature and can withstand 100°C for a long period, but isn't an intestinal pathogen.

Adolescents and adults probably will do fine with just filtered water. But nothing beats boiled water for microbiologically safe water. Howard Zucker, MD from the Department of Health, New York advised the provision of boiled drinking water for infants, children or the elderly with a frailer immune system.