18.الْكَهْف

اَوۡ يُصۡبِحَ مَآؤُهَا غَوۡرًا فَلَنۡ تَسۡتَطِيۡعَ لَهٗ طَلَبًا‏

Or its water may sink so deep into the earth that it gets beyond your means to fetch.’