I want to execute goblins by throwing them into the sea and WATCHING THEM SLOWLY DISSOLVE INTO PILES OF GOO AND BONES AS THEIR SKIN BECOMES COVERED IN GREEN GLASS.
Think of this, you can always make execution cells that are seasonally plagued (depending on the ailment/location/associated plagues, according to alignment/biome). Torture them with the seasonal ailments that come with the waters when the time comes for them to take effect (again, based on the chances that they occur during the season. It's an uncommon natural occurrence).
You gotta admit, death by breathing in necrotic red tide, and following it up with the next season causing dizziness via soaking? Who can beat that? Of course, it doesn't always have to end up that way. Let's not forget, who doesn't want to fish copper fish or literal gold fish? Although they are just plated, but you can still collect the mineral deposit from the corpse/fishery/refuse. Of course, it'll have to be smelted from the raw material first (preventing fishing from being too relied upon for ore collecting).
There has to be other ailments than what I have listed that RT can cause. Plus, not all of them have to be bad. What about fanciful lands' versions of red tide having reactions similar to a fountain of youth (super speed or strength, healing waters)? However, drinking, skin exposure/swimming or breathing in the heavenly algae doesn't only affect you. What about wildlife and the unicorns? o_o;
Now that exposed well isn't such a bad idea anymore. As long as the water is exposed to the elements and is drinkable, or can be contaminated by the tides. Just remember to wall it in enough to protect the partiers.
I don't know if the RT plating effect should only affect scaly creatures (such as fish and sea monsters) or if it can also be used as a method of plating prisoners by making them swim in the stuff for a few weeks (to prevent escape, I would advise barring the floor or at least any way that leads out via swimming).
Although it seems a bit technologically advanced, I can imagine plating technology would allow for some rather cheap productions and could end up over-modernizing the game a bit. Just think, chrome-plated swords. Blind your enemy as you assault from a hilltop during sunrise (well, depending on where the sun is more like, relative to wielder).