Al-Kahf - 18:41

أَوْ يُصْبِحَ مَاؤُهَا غَوْرًا فَلَن تَسْتَطِيعَ لَهُ طَلَبًا
[18:41]
Or its waters should sink down into the ground so that you are unable to find it.
"Or the water of the garden will run off underground so that thou wilt never be able to find it."
Or some morning the water thereof will be lost in the earth so that thou canst not make search for it.