Is there a Mongolian (or Tengrist) ritual of throwing water in front of someone before they set off on a journey? Or is that just a Turkish thing?
As a Mongolian, the first thing to come to mind is, spraying milk right after someone special such as a family member leaves. For book sources. I believe it was described by Jack Weatherford in "Genghis Khan and the Making of the Modern World" or "The secret history of Mongol Queens". I find this interesting as "suu" means milk in Mongolian and water in Turkish, if I'm not mistaken.
This is definitely a Tengrist ritual that - as many others - is foundin both Muslim and Christian countries that have Tengrist past. Tengrism gradually integrated in both Christianity and Islam. There are also a number of rituals revolving around 40 days - 40 days after a child is born and 40 days after someone has died. They are very common in the Balkans and in the Arab world - and people usually think that they are Christian or Muslim - they are in fact Tengrist and have been brought in Europe separately by the Bolgars and by the Turks. Usually, as a rule of thumb, rituals that are common both in the Balkans and in the Middle East, are of Tengrist origin.