Just as filtration and chlorination made drinking water safe at scale, we now have the tools to do the same for indoor air: ventilation, high-quality filters, and germicidal light. A century ago, germicidal light at 254 nanometers seemed to be a promising way of controlling pathogens by killing them in the air, but it turned out to cause irritation and cancer in the skin, and it was largely dropped when antibiotics became widespread. But today there is an update that has none of these drawbacks. We now know that wavelengths under 230 nanometers, especially 222 nanometer light, are harmless to humans, but can still disable microscopic pathogens. We know how to filter out all wavelengths except the ones we want, and how to direct them away from humans, cycling the air through them to clean it without exposing people to it, just in case it carries unknown risks. This far-UVC light, as it is called, may be how we can make the air we breathe as safe as the water we drink.