Sea Critters

[Armchair detective]

I got to thinking about how battery testers work, you know, the kind where you draw fluid from each cell. Depending on how far up the indicator sat in the tube, it would indicate the ability to hold a charge in each cell. This is actually a measure of the density of the fluid, a proportion of sulfuric acid to water.
It seems to me that this idea could be used to determine the water to seawater ratio, although such a device would have to be extremely sensitive. Get samples from these water holes on the island, test 'em. Samples with seawater? You got a flood tunnel.

 

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