Islamic concepts

Tayammum — purification without water

alternative hygiene ritual (before worship) when far away from clean water

Tayammum is an alternative to Wudu when you don’t have access to clean water. (roughly 1.9 km or 1.2 mile)

In developed countries, clean water is widely available. The situation where Tayammum would be allowed hardly presents itself in daily life. It might come up when going camping.