The empty space in porous rocks can store liquid or gas.
Reservoir rocks are rocks that have the ability to store fluids inside their pores, so that the fluids (water, oil, and gas) can be accumulated.
So water is one of the fluids that these rocks can store. However this was portrayed in the Quran 1400 years before it was discovered.
٧٤ ثُمَّ قَسَتْ قُلُوبُكُمْ مِنْ بَعْدِ ذَٰلِكَ فَهِيَ كَالْحِجَارَةِ أَوْ أَشَدُّ قَسْوَةً ۚ وَإِنَّ مِنَ الْحِجَارَةِ لَمَا يَتَفَجَّرُ مِنْهُ الْأَنْهَارُ ۚ وَإِنَّ مِنْهَا لَمَا يَشَّقَّقُ فَيَخْرُجُ مِنْهُ الْمَاءُ ۚ وَإِنَّ مِنْهَا لَمَا يَهْبِطُ مِنْ خَشْيَةِ اللَّهِ ۗ وَمَا اللَّهُ بِغَافِلٍ عَمَّا تَعْمَلُونَ
Rocks crack and water comes out of them.
How could an illiterate man who lived 1400 years ago have known that rocks can store water?
The Quran (Koran, the book of Islam) contains scientific knowledge that could not have been known 1400 years ago. It ranges from basic arithmetics to the most advanced topics in astrophysics. You are invited to go through those miracles and judge for yourself.