When the comets enter our atmosphere the heat generated on entry vaporizes this ice into the atmosphere.
Origin of water on Earth
Comets, trans-Neptunian objects, or water-rich meteoroids (protoplanets) from the outer reaches of the asteroid belt colliding with Earth may have brought water to the world's oceans. Asteroids may have been primarily responsible based on several studies, including measurements of the ratio of the hydrogen isotopes deuterium and protium, since similar percentage impurities as in carbon-rich chondrites were found in oceanic water, whereas previous measurement of the isotopes' concentrations in comets and trans-Neptunian objects correspond only slightly to water on Earth. In January 2018, researchers reported that two 4.5 billion-year-old meteorites found on Earth contained liquid water alongside a wide diversity of deuterium-poor organic matter.
The Christian Bible says that God created water directly on Earth, however the Quran didn't do this mistake instead it says that God sent down water from outer space and then made Earth its dwelling:
And We sent down water from the heaven in proper quantity, and we made Earth its dwelling, and We are Able to take it away.
١٨ وَأَنْزَلْنَا مِنَ السَّمَاءِ مَاءً بِقَدَرٍ فَأَسْكَنَّاهُ فِي الْأَرْضِ ۖ وَإِنَّا عَلَىٰ ذَهَابٍ بِهِ لَقَادِرُونَ
If God made Earth its dwelling (فَأَسْكَنَّاهُ فِي الْأَرْضِ ) then this means that water formed in outer space. In another verse the Quran explains how water came down from outer space.
In the creation of the heavens and the earth; in the alternation of night and day; in the ships that sail the oceans for the benefit of mankind; In the water which Allah sent down from the Heavens and brought with it life to Earth after being dead and gave life in it to every kind of land animal; And in directing the winds; And in the clouds that are enslaved between the Heavens and the Earth; [All these] are Signs for a people who comprehend.
١٦٤ إِنَّ فِي خَلْقِ السَّمَاوَاتِ وَالْأَرْضِ وَاخْتِلَافِ اللَّيْلِ وَالنَّهَارِ وَالْفُلْكِ الَّتِي تَجْرِي فِي الْبَحْرِ بِمَا يَنْفَعُ النَّاسَ وَمَا أَنْزَلَ اللَّهُ مِنَ السَّمَاءِ مِنْ مَاءٍ فَأَحْيَا بِهِ الْأَرْضَ بَعْدَ مَوْتِهَا وَبَثَّ فِيهَا مِنْ كُلِّ دَابَّةٍ وَتَصْرِيفِ الرِّيَاحِ وَالسَّحَابِ الْمُسَخَّرِ بَيْنَ السَّمَاءِ وَالْأَرْضِ لَآيَاتٍ لِقَوْمٍ يَعْقِلُونَ
So the water itself came from the heaven above the clouds. Here God is not talking about rain (matar or wadk in Arabic) instead God is talking about water (مَاءٍ).
In another verse, the Quran says that water originally came from the heavens above the clouds in the form of ice. There are mountains in the heaven that have ice inside them; those mountains could fall on Earth making a very bright flash:
Can't you see that Allah makes the clouds move gently, then joins them together, then makes them into a pile? Then you see rain come out from within? And He sends down from heaven mountains with ice inside them; that strike whomever He wishes or miss whoever He wishes; Its flash almost blinds you.
٤٣ أَلَمْ تَرَ أَنَّ اللَّهَ يُزْجِي سَحَابًا ثُمَّ يُؤَلِّفُ بَيْنَهُ ثُمَّ يَجْعَلُهُ رُكَامًا فَتَرَى الْوَدْقَ يَخْرُجُ مِنْ خِلَالِهِ وَيُنَزِّلُ مِنَ السَّمَاءِ مِنْ جِبَالٍ فِيهَا مِنْ بَرَدٍ فَيُصِيبُ بِهِ مَنْ يَشَاءُ وَيَصْرِفُهُ عَنْ مَنْ يَشَاءُ ۖ يَكَادُ سَنَا بَرْقِهِ يَذْهَبُ بِالْأَبْصَارِ
God sent down from the heaven (above the clouds) mountains with ice inside them!!! The clouds are enslaved between the Heaven and the Earth but the water itself originally came from the Heaven above the clouds in the form of ice in mountains. They make a bright flash; but this is the same description of comets and meteors when they hit our atmosphere.
Water covers about 71% of Earth's surface. This is also the same ratio the word "Sea" and word "Land" appear in the Quran. "Sea" 32 times and "Land" 13 times. The ratio of "Sea" to the total (Sea + Land) = 32/(32+13) = 71%.
(The rainbow is a phenomena caused by the interaction of light with water droplets. The characteristics of light and how it interacts with other substances didn't change since the Big Bang, 13.7 bln years ago. But according to the Bible God created the Rainbow only 4000 years ago at the time of Noah. Genesis 9:12-13).