[bluGill]

> Do they boil their water? Doesn’t it help with disease?

Maybe. We need to specify what makes exactly makes some water sample unsafe before we can discuss anything. Sometimes boiling helps, sometimes it makes it worse. If your concern nitrates, lead, arsenic, or other things that won't boil, then boiling just concentrates the contaminates and makes the water worse! If your concern is bacteria boiling will kill the bacteria, but the dead cells are still there which may include some poison in the bacteria.

Most filters will not remove the above either. Water is very good at dissolving a lot of nasty things that you don't want in your body (that ability enables a lot of controlled chemistry and thus life as we know it!), and once dissolved it will go through a filter. We again need to know exactly what is in the water before we can discuss if a filter works or not, otherwise we should just assume the filter is not going to make water safe.

[rtkwe]

Most of the time boiling for water purification just means bringing it briefly to a boil to kill pathogens not boiling for an extended period so there's only minimal water loss so very little concentration actually happens.