comrade1234 parent
No mention of the freshwater source... line from the shore? Shipped in?
The listing says it has "a 250,000 litre rain harvest system and storage with a reverse osmosis system providing potable water".
Shipped in surely, everything else would need to be anyway. The flushing toilets etc. mentioned as a challenge probably use a rainwater collection system or perhaps seawater (I'm not sure if the latter's done, desalination probably necessary?).
You can run toilets on seawater just fine, maybe some slightly different seals.
The listing mentions a 30,000 gallon reservior, so I imagine rainwater collecion from the "parade ground".
That'd be my guess also: https://britishlistedbuildings.co.uk/300017169-thorne-island...
The British Listed Buildings site has photos of the fort and boat approach with stairs, picking crane, and sloped ladder lift for getting loads from water to gate.