If most tap water in the U.S. is safe to drink, why are engineers and scientists still doing so much research on drinking water, and why is the federal government thinking about more regulations?

In short, yes it is possible. Here's how...if a raw water source contains arsenic below the drinking water standard, water utilities do not generally attempt to reduce or remove this arsenic from the treated water supply before it enters the distribution system. Through co-precipitation with iron or other chemical processes, some of this arsenic tends to accumulate in pipe scales or build up as a film on iron-containing components throughout the distribution system.

But likely you should be more concerned if your source water is ground water instead of surface water.

Because arsenic occurs naturally in rocks and soil, water, air, and plants and animals, it can be further released into the environment through natural activities such as volcanic action, erosion of rocks and forest fires, or through human actions. Approximately 90 percent of industrial arsenic in the U.S. is currently used as a wood preservative, but arsenic is also used in paints, dyes, metals, drugs, soaps and semi-conductors. High arsenic levels can also come from certain fertilizers and animal feeding operations. Industry practices such as copper smelting, mining and coal burning also contribute to arsenic in our environment. Higher levels of arsenic tend to be found more in ground water sources than in surface water sources (i.e., lakes and rivers) of drinking water.

The demand on ground water from municipal systems and private drinking water wells may cause water levels to drop and release arsenic from rock formations. Compared to the rest of the United States, western states have more systems with arsenic levels greater than EPA’s standard of 10 parts per billion (ppb). Parts of the Midwest and New England have some systems whose current arsenic levels are greater than 10 ppb, but more systems with arsenic levels that range from 2-10 ppb. While many systems may not have detected arsenic in their drinking water above 10 ppb, there may be geographic "hot spots" with systems that may have higher levels of arsenic than the predicted occurrence for that area.

If you feel your water source may be exposed to arsenic it's best to get your water tested. It's also important to note the effects of arsenic. Human exposure to arsenic can cause both short and long term health effects. Short or acute effects can occur within hours or days of exposure. Long or chronic effects occur over many years. Long term exposure to arsenic has been linked to cancer of the bladder, lungs, skin, kidneys, nasal passages, liver and prostate. Short term exposure to high doses of arsenic can cause other adverse health effects, but such effects are unlikely to occur from U.S. public water supplies that are in compliance with the arsenic standard.

With water processing changes, including chlorination, some of this arsenic that has built up can be re-suspended or dissolved back into the water to cause customer’s tap water to exceed the U.S. EPA drinking water standard for arsenic. The Environmental Protection Agency is funding research efforts to fully understand exactly what is going on with the build up and release of arsenic in water distribution systems.