Colorless, tasteless, and odorless. Such are the features of a naturally occurring element in the mineral deposits of Earth. This element is arsenic.
When water goes through underground aquifers, it usually dissolves inorganic substances from these mineral deposits, and one of these is arsenic. While it might sound safe to drink arsenic-contaminated water (after all, arsenic is colorless, tasteless, and odorless), it actually is very dangerous. Prolonged exposure to this kind of water can cause many diseases as well as many types of cancer, which could result in death.
Unfortunately, many regions don’t have the necessary equipment to treat their water through conventional means, and so they don’t have a choice but to use arsenic-contaminated water, which expose them to the risks mentioned above.
The crisis of widespread arsenic contamination, particularly in rural South Asia, has been described as the largest mass poisoning in human history.
Researchers, fortunately, have finally found a way to filter arsenic-contaminated water in a cheap way: by using rust.
More details about this over at PHYS.org.
(Image Credit: Tomihanhdorf/ Wikimedia Commons)