From a lake
In most communities, tap water is safe for drinking.
Most people in Bhutan get their water from either a house tap or occasionally a village tap.
It's about the same. Most bottled water IS tap water, so any chemicals and weird stuff in tap water are in bottled water too.
Depends on what company you're comparing tap water to. But most bottled water companies use filtered water (the same as tap water). In most cases bottled water is not purer than tap water. Note that tap water is not the same everywhere, not are all brands of bottled water the same. But legal requirements for water purity are the same for tap water as for bottled water. In some cases, bottled water actually is tap water, that has simply been taken from the tap and put into bottles.
Tap
Most likely salt water. Depending on the chlorine levels in the tap.
Most deserts will expand, and many farming communities will be abandoned. Also many conflicts would arise, if drinking and tap water becomes scarce.
A water filter will remove MOST contaminants. However it does not remove all contaminants from tap water. There is not a water filter out there that can remove every single contaminant from your tap water.
In most places "potable".
you can tap tap
No, it isn't faster, tap water freezes just at the same temperature as tap water
tap water...