ἀποδεικτέον
From LSJ
βορβόρῳ δ' ὕδωρ λαμπρὸν μιαίνων οὔποθ' εὑρήσεις ποτόν → once limpid waters are stained with mud, you'll never find a drink
English (LSJ)
A one must show, proue, Pl.Phdr.245b. 2 c. dupl. acc., one must make one so and so, σκαπανέα αὐτὸν ἀ. Luc.Vit.Auct. 7.