Brown, silty streams, tea-colored rivulets, even clear, ice-cold lakes—any backcountry water source can serve up a cocktail of contaminants. But not everything that’s present in an undeveloped water source is necessarily harmful, and only some things pose an immediate threat to your health. In fact, it’s impractical and unnecessary to remove everything, all the time. So, in terms of backcountry water treatment, when is water considered safe to drink? First, what’s commonly in backcountry water? The types of contaminants that make water “dirty” depend a lot on that source’s surrounding environment. But most contaminants can be placed into these categories: Microorganisms—Simply put: tiny bugs or germs. Microbes are the primary focus of treatment devices because of their immediate and potentially serious risk to your health. The pathogenic ones include bacteria…