Said Rab Judah in Samuel's name, He means this: One may not prepare a large quantity of salt water, but one may prepare a small quantity of salt water.
Well, that gets a little tricky to define. But, maybe it’s not quantity but quality?
R. Judah b. Habiba recited: We may not prepare strong salt water.
Ok – now define “strong” salt water:
Rabbah and R. Joseph b. Abba both say: Such that an egg floats in it.
And how much is that? — Said Abaye: Two parts of salt and one part of water.
This reminds us of the Dead Sea! Funny you should mention it. . .
When R. Dimi came, (to Babylon from Palestine) he said: ‘No man ever sank in the Lake of Sodom.’
R. Joseph observed: Sodom was overturned and that statement was overturned! ‘No man sank in it’ – but, what, a plank of wood did?
R. Joseph’s sarcastic comment is countered by Abaye:
He states the more surprising thing. It is unnecessary [to mention] a plank, seeing that it does not sink in any water; but not even a man, who sinks in all [other] waters of the world, [ever] sank in the Lake of Sodom.
All of this is necessary as an discussion of the healing properties of the Dead Sea (considered so even today!). Since healing a wound is not permitted on Shabbat (unless it is life-threatening) because we might be tempted to crush medicines, etc. – what about using the healing properties of the salt water?
it once happened that Rabin was walking behind R. Jeremiah by the bank of the Lake of Sodom, (modern “Dead Sea)” [and] he asked him, 'May one wash with this water on the Sabbath (in order to heal)?'
'It is well,' he replied.
'Is it permissible to shut and open' (one's eyes with drops of Dead Sea water in order to heal them?)
'I have not heard this', he answered, [but] I have heard something similar:;. . .one said: [To put] 'wine into one's eye is forbidden; [to put it] on the eye, is permitted.'
Dead Sea water applied directly in the eye (ouch!) could only be for healing. Around the eye (less ouch!) could be for other reasons. That is to say: if the purpose is not obviously one of healing, - maybe you’re just bathing in the salt water - it is permitted. But if it is applied directly for healing, it is not.
This is not just about Dead Sea water, but other things which can be "dual purpose" - for healing and for other uses. Ambiguity matters!