[Pseudoscience-is-malarkey (OP)]

Is desalinated ocean water just as healthy and potabile for human consumption as purified spring, rain, lake, and melt water? Is the issue with treated salanated and brine water primarily cost?

Also, in regards to freshwater, what should we look out for before drinking it?

[alancalverd]

Yes.

The fact that you have to purify spring, rain. lake or melt water suggests (correctly) that they all contain pathogens to some extent.

If you have to drink surface water, take it from the highest point of the source where it is least likely to have had contact with the corpses or waste products of birds and mammals. I have a photograph in my archives somewhere, of a dead sheep floating on one of the more beautiful English lakes, next to a notice "this is a public drinking reservoir - swimming is prohibited".

Mineral water generally contains fewer pathogens than surface water, but all sorts of inorganic toxins can be inadvertently added during processing in a bottling plant. I remember when Perrier was recalled (I was on a process quality control course at the time- how we laughed!) because it was contaminated with benzene.  And beware of any advertised health benefits: some (e.g Volvic) claim to be healthy because they contain almost no solutes , whilst others claim to be bursting with "vital" inorganics.

The last time I read any credible literature on the subject, New York tap water was cleaner than any bottled product. Sadly, UK tap water has now been reduced from publicly-owned industrial quality (essentially, H2O with a whiff of chlorine and fluoride) to European standards for private supplies, and is not fit for use in hospitals or process industries. Look out for state or municipal ownership.

[Origin]

Is desalinated ocean water just as healthy and potabile for human consumption as purified spring, rain, lake, and melt water?

Yes.

Is the issue with treated salanated and brine water primarily cost?

Yes.

Also, in regards to freshwater, what should we look out for before drinking it?

In general do not drink water out of puddles, lakes and rivers.

[Bored chemist]

All fresh water is desalinated ocean water.
Sometimes the desalination process involves the sun + clouds etc.

[Bored chemist]

Essentially all fresh water is desalinated ocean water.
Sometimes the desalination process involves the sun + clouds etc.

[jasonlava]

 I'm no expert, but from what I've gathered, desalinated ocean water can be safe to drink, but it might lack some minerals that you'd find in other sources. Cost could be a big factor, but there's also the environmental impact to consider with the byproducts.

[evan_au]

desalinated ocean water can be safe to drink, but it might lack some minerals that you'd find in other sources

You could try adding a bit of the untreated sea-water back into the desalinated seawater - most minerals from other sources end up in the sea!

[Zer0]

& then Obviously boil the Concoction at over 102 degree Celcius before sipping into it.

*Note* - avoid all such crazy survivor in the wild stunts at all costs n simply carry bottled water.
The so called " Survival Experts " on the Telly are PHONY!