Filtering your home's drinking water may be more complicated than you expect. Different products filter out different contaminants such as chlorine, heavy metals like lead, or fluoride, so evaluating and comparing them is difficult.

Researchers at Ohio State University are trying to make things simpler, particularly for people worried about toxic chemical compounds left by bacteria, a problem that led the drinking water in Toledo, Ohio to be shut off in 2014.

The team used contaminated water from Lake Erie, which they also diluted so they could test two different concentrations of microcystins.

When you’re getting water from a municipal system, you usually know about the contaminants and chemicals in your water since water utilities are required to share this information with their customers. The same is true of potentially harmful bacteria, viruses or parasites. They have generally either been killed or filtered out of tap water by the local utility.

In the case of the bacteria affecting the Toledo water supply, however, in which bacteria in a bloom of algae was sucked into the municipal water supply, residents couldn't even resort to boiling their tap water because the chemicals affecting it, microcystins, are resistant to heat and boiling the water merely concentrates them. Microcystins affect the liver, where they accumulate and can clog the organ.

Harmful bacterial blooms, such as those behind the water problems in Toledo, are a major environmental problem in all 50 states. And they're on the rise as more and more nutrients, particularly phosphorus and nitrogen, are making their way into the bodies of water tap water comes from.

Pitcher Report

Researchers tested three water-filter pitchers to see how well they removed microcystins. And while they don't name brands, they do offer several recommendations consumers will find useful. The team used contaminated water from Lake Erie, which they also diluted so they could test two different concentrations of microcystins.

All three pitchers tested used activated carbon, which traps particles on its surface and in pores. The more slowly a pitcher filtered the water, the more toxins it removed. Expensive pitchers did a better job than less expensive brands, at least among the models tested, whose prices ranged from $15 to $50.

“Because drinking-water treatment plants also use activated carbon, I figured that these home filters might also remove some microcystins, but I wasn't expecting results this good and such big differences among the pitchers,” said Justin Chaffin, the study's lead author and a senior researcher and research coordinator at Ohio State's Stone Laboratory, in a statement.

The best pitcher left no detectable toxins in the water. The least effective filter removed at most 50 percent of the contaminants in different trials. The pitcher that used activated carbon solely derived from coconut did not work as well as the two that used activated carbon from a blend of sources.

Slower filtration worked better — it kept the toxins in contact with the carbon filter longer and gave the filter more time to trap them.

I figured that these home filters might also remove some microcystins, but I wasn't expecting results this good and such big differences among the pitchers.”

Water-filtering pitchers could be used as a safety net by people worried about microcystins going undetected at the water treatment plant, Chaffin suggests, but, he adds, it is not a good idea to rely on them when people are being warned to drink only bottled water (or water from another source). There is no guarantee that a pitcher filter could remove enough toxins to make water, as contaminated as Toledo experienced, safe to drink.

Filters that use activated carbon are good at removing chlorine and organic (carbon-containing) compounds from drinking water. The activated carbon in the filter “grabs” bad things from the tap water as they bind to the carbon molecules. Most of these filters remove little, if any, bacteria, heavy metals such as lead or fluoride ions.

The team also checked to see if the microcystins might re-contaminate water if the filters were used after they had expired. They ran ultra-clean de-ionized water through the purifier and found there were no microcystins at all in that filtered water, making it pretty clear that the contaminants that are removed are stuck to the filter for good.

Because they remove chlorine and fluoride, pitchers with activated carbon filters can be attractive to people who are concerned about the odor or taste of tap water; but it is unclear why families might want to remove fluoride from their water, since it helps prevent tooth decay.

And while filter costs can add up over time — a family of four may need a new filter as often as every two weeks — the study found filters were more economical in the long run than buying bottled water. They're also better for the environment because you're not adding to the mountain of empty bottles polluting shorelines.

The study appears in Water Science and Technology: Water Supply and is freely available.