Indonesian adrift surviver water situation

Question

This story is of a teenager who got lost at sea for 49 days before getting rescued. As to how he stayed alive:

He survived by cooking fish he caught and sucking water through his shirt to remove some of the salt.

Catching fish is reasonable given the right equipment, and cooking wouldn't even be strictly necessary in a survival situation. However, a T-shirt will not remove any salt from sea water. To do so requires a special membrane and very high pressure.

It seems more likely that he used a reverse-osmosis hand-pump such as this one or a solar-powered pump.

Alternatively, he may have captured fresh rainwater in his shirt, dependent on the monsoon.

It may be possible to breathe the vapor from sea-water soaked clothing to humidify the air and slow dehydration (the salt doesn't evaporate into the air), but that seems like it wouldn't be enough to make it 49 days. Such a system would be similar to this concept.

Is there a more reliable source of information on how he got his water?

Answer 1

There's not a lot of information out there (and what we do have is all news quality so I'm not inclined to completely trust it), but what we do have suggests that he didn't start drinking saltwater until later on. He started out with some food and water on his "floating hut":

The craft’s owner, who had about 50 floating huts in the area, would send someone each week to collect the fish in his trap and drop off food, water, lamp fuel and other supplies.

[...]

The ingenious teen knew that running out of water could be his demise, so he was frugal with his supply, granting himself only three sips a day.

When his water supply ran dry and it hadn’t rained for a long time, “he drank by sipping water from his clothes that had been wetted by seawater,” Mirza said.
_{Story behind teen’s incredible survival after being stranded at sea}

It's more explicitly claimed in other articles (example) that he also drank rainwater when possible. We don't know how much salt water he actually consumed.

Answer 2

WDTV.com says:

Within a week, Adilang said he ran out of food and survived on the fish he caught and cooked using wood from the raft. He drank rainwater and according to one report, strained seawater through his clothes to drink.

When he ran out of his water stores and if he (apparently) didn't have any water desalination device, he had only two options to survive for 49 days:

• to drink rainwater (what he probably did)
• to distil seawater by boiling it and catching the vapour (no one mentioned this)

You can't remove any meaningful amount of salt from seawater by straining it through any type of usual cloth, because the size of a sodium (Na) atom is only 227 pm (pm = picometer = 10 ^-12 m) (Periodictable.com).

Drinking any amount of seawater just makes you more dehydrated, because your kidneys can remove the excessive salt only by removing more water than you get from seawater.

Thus for every liter of seawater drunk, 1.5 liters of urine volume would be required to rid the body of 1,200 milliosmoles of sodium chloride ingested in addition to 600 milliosmoles of other solutes such as urea. (Hall JE, The Guyton and Hall Textbook of Medical Physiology, 13th Edition, 2016, p.373)

You also can't get net water by eating fish, which is high in protein, because urea, the breakdown product of protein, when excreted, drags more water into the urine than you got from fish, as explained on Outdoors SE.