On the picture: The ‘Şadırvan’ of the Yıldırım Mosque. It has been restored close to its original 15th century style.

A şadırvan (from the Persian ‘sadirvan’) is a type of fountain that is usually built near the entrance of mosques or other buildings where common prayer can be held, with the main purpose of providing water for drinking or ritual ablutions to several people at the same time, but also as decorative visual or sound element.
It is a typical element of Ottoman architecture. It is also called ‘abdest alma çeşmesi’ (= fountain for ablutions).

Ritual ablutions: ‘Wudu’ (Arabic: الوضوء‎ al-wuḍūʼ) or in turkish: ‘abdest’?is the Islamic procedure for washing parts of the body, typically in preparation for formal prayers. The turkish word is from Persian origin (âb = water & dest = to take) and was introduced in Seljuk times (11th – 13th century).
For Sunni muslims, the procedure (which can be characterised as ‘small washings’) consists of four actions:
Washing the face once; washing both arms including the elbows once; performing ‘masah’ of one-fourth of the head; washing both feet once up to and including the ankles.
‘Masah’ of the head: wet hands should be passed all over the head, with a deliberate stroke downwards from the top of the head; then index fingers are placed in ear canal while thumbs pass behind the ears and lobes; then swipe back of hands over neck nape. This is done in one continuous motion, without refreshing the hands with water for each component.

Correspondent: J.M.Criel, Antwerpen.
Sources: (among others) Wikipedia.