The water, according to everyone who has recorded an opinion on the matter, remains fresh regardless. This is the Chink Well, and the name itself is a clue to its purpose: "chink cough" was the local term for whooping cough, and the well's reputation as a cure for that illness is what drew people to it, including, apparently, a considerable number of children whose parents were willing to navigate a coastal cave to find it.

The well sits below the boundary wall of Portraine Demesne, deep inside the cave system. Folklore gathered from Swords schoolchildren and recorded in the Irish Folklore Commission's Schools' Collection (Volume 0789, Pages 267-8) describes it as "a scooped hole in a rock, which always supplies fresh spring water," and goes on to explain the local account of why it stays fresh despite the tide: during the Penal period, when Catholics in Ireland were legally prevented from practising their religion openly, priests were said to have celebrated Mass in these caves. Finding themselves without a reliable water source, they prayed, and the spring that appeared was held to be miraculously preserved from the salt of the surrounding sea. A second account, collected from Malahide schoolchildren and recorded in Volume 0791 of the same collection, notes more plainly that the field above the cave was at that time owned by the Portrane Asylum, and that the well had cured a great number of children of whooping cough. The cave above is said to provide an alternative entrance from the adjoining cave system.

Access to the Chink Well depends entirely on the tide. It can only be reached at low tide, which means consulting tide tables before setting out along the coast near Portrane. The cave sits below the demesne wall, so the approach is along the shoreline rather than through any formal entrance. Once inside, the well itself is not a constructed feature in the usual sense; there is no stonework surround or carved basin. It is simply a hollow worn into the rock, fed by a spring that has been doing precisely what springs do, quietly and without interruption, regardless of what the sea is doing around it.