This assumes that people have adequate access to the energy required for boiling and have the necessary equipment to do so.

Not at all an insignificant amount of energy btw.

Keep in mind, there are also many illnesses and diseases that can be caused by inorganic content in water that no amount of boiling will make potable and can cause everything from poisoning to cancer long term (lead, etc).

To be fair, waterborne illness is very often organic related: microbes, viruses, bacteria, etc.

No boiling required. Enough plastic bottles and a sunny day works too.

Even if heating with gas/electricity, aiming for boiling is hard to screw up, but an overshoot of what’a required.

This is only good for bacteria/viruses.

Purification tablets are also not that expensive compared to the effects of crippling diseases.

Crippling disease is free if you don’t get any medical care.

You’re forgetting the opportunity cost.

You have to have opportunities to have opportunity cost.