Modern home water filtration systems are pretty amazing. Your municipal water authorities clean public water as best they can, but a simple filter or reverse osmosis drinking water system can get it even cleaner. Today, more than four out of ten Americans use a water treatment unit in their home, inspiring confidence that they have better water. But can you be too over-confident in your home water quality? Yes.

Filtration systems can do a lot, but there are some water hazards even the best home or commercial water filtration system can’t entirely fix. If any of these emergencies happen with your water supply, remember that you may need a solution beyond your typical water filter.

A Boil Water Advisory

A boil advisory was just experienced in early summer 2018 in Washington, D.C. when a pump in the city’s water filtration system temporarily lost pressure. While a boil advisory could happen for any number of reasons, it means public officials suspect tap water could be unsafe. Typically, a boil advisory indicates problems that can’t be fixed by your typical home water filtration system, even by a sophisticated reverse osmosis drinking water system. The only way to reliably destroy potentially dangerous protozoa, bacteria, and viruses in your contaminated tap water is to boil it before use.

A Do-Not-Drink Advisory

Salem, Oregon recently experienced a Do-Not-Drink advisory in May 2018 when small amounts of cyanotoxins, a toxic kind of algae, were detected in the municipal water source. The number of cyanotoxins in the water remained at levels that were safe for most adults but considered potentially dangerous for children under six and other vulnerable populations. While city officials took care of the unusually aggressive algae bloom that caused the advisory, they warned what manufacturer’s instructions will also inform you: that most filters will not eliminate cyanotoxins from your drinking water.

Herbicide and Pesticide Contamination

A reverse osmosis drinking water system doesn’t allow anything larger than water molecules to pass through. It filters out plenty of heavy metals like lead, asbestos, and radium. What it doesn’t filter out? Pesticides. India is having an ongoing issue with possible pesticide contamination in its groundwater; if you live in the U.S., especially in rural farming areas with well water sources, it’s a risk for you as well. The tiny town of Coates in Dakota County, Minnesota is one such rural area with well water issues. If you have well water, you’ve likely already had it regularly tested for quality. If it had a high concentration of nitrates, for example, there are ways to professionally remove the nitrates. Boiling or using a filter will not remove them.

To reiterate, filters can do a lot of good for your water. They can remove lead, chlorine, and sediments. But you should also be aware of the few emergency-level drinking water situations that your trusty filter cannot handle. Keep an eye out for emergency alerts concerning your water supply from your city or county, and if you have a well, get it inspected and professionally treated often.