Real Bible Translation

Julia Smith Literal 1876 Translation:
The fig tree, my brethren, cannot make olives, or the vine, figs: so no fountain can make salt and sweet water.

LITV Translation:
My brothers, a fig tree is not able to produce olives, or a vine figs. So neither can a fountain produce both salt and sweet water.

Footnotes

When in Doubt, Change it!

When The earliest Greek witnesses (Nestle 1904, WH 1881, Tischendorf 8th) clearly have:

οὔτε ἁλυκὸν γλυκὺ ποιῆσαι ὕδωρ

while later or Byzantine-influenced forms (RP, Textus Receptus, GOC editions) modify it into:

οὐδεμία πηγὴ ἁλυκὸν καὶ γλυκὺ ποιῆσαι ὕδωρ
(no spring can produce both salty and sweet water).

That means modern translations (based mostly on the Byzantine majority or TR tradition until recently) rendered the modified versions rather than the original compressed Greek of the earliest witnesses.

ποιῆσαι is an aorist active infinitive (“to make, to do”), not passive.

Thus the sense is:

“Nor to make salty water sweet.”

The difficulty is that Greek here uses accusative + predicate accusative with an infinitive, without an explicit subject. Translators of the Byzantine/TR form supplied πηγή (“spring”) as subject: “No spring can make both salty and sweet water.”

But in the earliest authoritative texts, we should understand an implied subject from the preceding clause (συκῆ … ἄμπελος …), so that the construction is elliptical:

“A fig tree cannot make olives, nor vines, nor to make salty water sweet.”

The difficulty in understanding the awkwardness of this compressed accusative-infinitive is probably why later scribes changed it into “no spring can …” phrasing.