Historical clue formulations

• Make potable, in a way — 2018-08-31
• Make potable, as sea water — 2004-10-11
• Treat, as seawater — 2002-08-28
• Make drinkable, in a way — 2001-02-03
• Make potable, in a way — 1999-09-16
• Make potable, perhaps — 1998-09-03
• Make ocean water drinkable — 1994-08-28