Suddenly, water filters are in the news. Legionnaires’ disease kills one tourist and sickens two others, the Legionella bacteria is found in the water at Miami’s Epic Hotel and Residences, and we are told that the hotel was using a powerful filter that stripped its water of protective chlorine and made it susceptible to such bacteria.

Reasonable questions arise: What about the water filter in my kitchen sink? Is it doing more harm than good? How common is it in the first place for big hotels to filter their water, and why do they do it?

First, experts say, there’s nothing wrong with filtering. It can be beneficial, even when the municipal water that enters a home, hotel or condo tower meets all the state and federal standards for quality.

“Filtering can be very effective and healthy,” says Dr. Bill McCoy, chief technology officer for Phigenics, an Illinois-based water safety consulting firm with clients around the world. “It can improve the water’s quality.”

The biggest reason people filter water is to remove its chlorine, improving its taste, he says. But filters also remove other contaminants — organic compounds including algae, plus dirt and debris that can exist even in water well-treated by municipal plants. Such contaminants can hurt both the flavor and clarity of water, McCoy says.

Water filters aren’t limited to hotels and other commercial buildings. Plenty of individual homes have them. There are “whole-house” systems and “kitchen sink” systems.

WHOLE HOUSE

Whole-house systems, which cost about $1,000, include small tanks sitting outside the house using activated carbon to filter all the water that enters.

“They take out the basics — chlorine, color and so on. A lot of people don’t like to shower in water that smells of chlorine,” says Jim Colman, environmental consultant at Water Purification Products in Margate.

At the Epic Hotel, Miami-Dade health officials said powerful filters stripped the water of its protective chlorine, making it susceptible to waterborne pathogens such as Legionella bacteria. Though Legionella was subsequently found in the hotel’s water, it hasn’t been determined that the Epic was the source of the bacteria that sickened the tourists. That is still being investigated.

Such problems of bacterial build-up are unlikely in private homes, Colman says, because their simple plumbing systems have few places where water sits unused for long times to permit bacteria to build up. Still, he recommends changing whole-house water filters yearly and detaching them briefly every few years to let chlorinated municipal water flow through.

More common in homes are water filtering systems mounted beneath kitchen sinks, with a separate faucet above, used for drinking and cooking, Colman says. A typical unit consists of an activated carbon filter that removes chlorine and organic materials plus a reverse-osmosis membrane that removes minerals. Prices on those systems vary: Colman will put one in for you for $439, or sell you a do-it-yourself kit for $199.

Colman is no fan of small filters that attach directly to faucets atop the sink.

“You need enough activated carbon to get decent treatment,” he says. “These only have a couple of tablespoons.”

Water filters in refrigerators treating through-the-door ice and drinking water are pretty good, Colman says, as long as you change the filter according to manufacturers instructions.

Water filter pitchers are also OK, Colman says, as long as you change the filter often enough. Also, keep in mind that the water in the pitcher is now without chlorine. Keep it in the refrigerator.

And if you don’t change the filters as per manufacturers’ recommendations, such systems can do more harm than good, says Dr. Paul Chadik, professor of environmental engineering at University of Florida. “If the carbon isn’t replaced, bacteria will actually colonize the filter and thrive there.”

In big buildings like hotels, water safety experts say it’s rare, but not unheard of, to use filters that strip away the chlorine from water as it enters the building. It’s done in less than 5 percent of cases, estimates Brook Winter, regional manager for Phigenics.

“I take care of five-star [hotel] properties from New York City to Phoenix, and I don’t see it,” he said. “Most of them take the county water as it comes.”

It’s not a mistake to filter, McCoy stresses. Filtering can improve the water’s taste, appearance and quality, he says.

Still, that chlorine was put there for a reason. When water is treated at a municipal water plant, most of the chlorine added is used up in removing its contaminants. But a small “chlorine residual” is left in the water to help it fight any new contamination it might encounter in municipal water lines or once it arrives inside a building, McCoy says.

OVERALL PLAN

So any filtering must be done as part of a carefully managed overall plan that includes running the taps at intervals to make sure the unchlorinated water is kept clear of contaminants.

“Americans are used to thinking their water is completely safe,” McCoy says. “In many cases it’s not true. If you surveyed all hotels and hospitals and assisted-living homes in the country, about 20 percent would be colonized with Legionella bacteria, even if they’re not removing the chlorine residual.”

Such bacteria would be found in shower heads, water taps and elsewhere — almost always in quantities too small to cause illness.

Water heaters can be a problem if water sits in them for long periods of time. A heater might serve 100 rooms, but 10 of those rooms are used only once a month.

Ice machines can create pools of stagnant water that encourage bacteria, and freezing them doesn’t kill them — it just temporarily keeps them from growing, McCoy says.

Even if water entering the building has adequate chlorine, by the time it reaches the farthest end of the plumbing system, the chlorine can be consumed by contamination in the plumbing. Also, bacteria can grow in the stagnant water of dead ends in plumbing systems or in hotel rooms that have been vacant, the water in their pipes unused for weeks.

“Biofilms can form on the inside surface of the pipes. If you’ve ever put your finger inside a faucet you can feel it. That slime is bacteria,” McCoy says.

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Home water filters remove impurities such as bacteria, chlorine and floride from water by means of a fine physical barrier, a chemical process or a biological process. There are various types of water filtration systems.

Point-of-use filters

Filters for home use include granular activated carbon filters (GAC) used for carbon filtering, metallic alloy filters, microporous ceramic filters, carbon block resin (CBR) and ultrafiltration membranes. Some filters use more than one filtration method. Jug filters can be used for small quantities of drinking water. Some kettles have built-in filters, primarily to reduce limescale buildup.

Portable water filters

Water filters are used by hikers, by aid organizations during humanitarian emergencies, and by the military. These filters are usually small, portable and light (1-2 pounds/0.5-1.0 kg or less), and usually filter water by working a mechanical hand pump, although some use a siphon drip system to force water through while others are built into water bottles. Dirty water is pumped via a screen-filtered flexible silicon tube through a specialized filter, ending up in a container. These filters work to remove bacteria, protozoa and microbial cysts that can cause disease. Filters may have fine meshes that must be replaced or cleaned, and ceramic water filters must have their outside abraded when they have become clogged with impurities.

These water filters should not be confused with devices or tablets that are water purifiers, some of which remove or kill viruses such as hepatitis A and rotavirus.

Homemade water filters

Water filters can be made on-site using local materials such as grass, charcoal (e.g. from burned firewood), and sand. These filters have been used by soldiers and outdoor enthusiasts. Due to their low cost they can be made and used by anyone, including the poor, who often do not have access to safe drinking water. Regrettably such filters do little if anything to mitigate against pathogens and other harmful constituents and can give a false sense of security that the water so produced is potable.