The name of the lake is Lake Gnostos with a “g” from the Greek meaning “knowledge,” which makes sense, given that what was once lost is returned. This could mean that the lake returns knowledge to those who drink from it. My theory is that this water will play a role for SB characters remembering FTL.
Also found in my digging around that Nostos (in OUAT ep13 the siren was in Lake Nostos) is a Greek word meaning “homecoming” and is a theme used in Homer’s Odyssey, so I feel sure this perhaps goes with the something lost being found idea (a homecoming of sorts). A siren is also present in Homer’s Odyssey.
I don’t discredit that the word might be “nosotos,” but I have doubts, since after looking on other websites, the word in general use is “gnostos”.
Moreover, I think that Prince James (aka Prince Charming) will use the water from Lake Gnostos to restore Snow White’s memories of their love in FTL.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy