think that why only the water of Zam Zam was chosen to wash the sacred heart of the beloved Prophet صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم instead of other waters?

While mentioning the wisdom behind it, Ḥakīm al-Ummah, Mufti Aḥmad Yār Khan NaꜤīmī رَحْمَةُ الـلّٰـهِ عَـلَيْه states:

The beloved Prophet صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم was sleeping in the house of Sayyidah Umma Hānī bint Abī Ṭālib رَضِیَ الـلّٰـهُ عَنْهَا. Angels woke him up and brought him to the Ḥaṭīm of the KaꜤbah. Until now, he           صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم was still drowsy. Then, he صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم was washed there. Ghusl is given to the body of the worldly groom, but the beloved Prophet صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم is such a unique groom that his blessed heart was also washed. The water of Zam Zam is superior to all other waters as it started flowing from the blessed foot of Sayyidunā IsmāꜤīl عَـلَيْـهِ الـسَّـلاَم. That is why, this water was chosen for the washing. The blessed chest was filled with faith and wisdom. Then, it was sewed back. Faith and wisdom already existed in the blessed heart of the beloved Prophet صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم from beforehand. This took place to increase the extent of faith and wisdom.^[1]

Ḥakīm al-Ummah, Mufti Aḥmad Yār Khan NaꜤīmī رَحْمَةُ الـلّٰـهِ عَـلَيْه also states:

The blessed heart of the Beloved Prophet صَلَّى اللهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم was already enlightened, but now it became نُوْرٌ عَلٰی نُوْر . The gold was from the Paradise. The water was of Zam Zam. Water of the Ḥaram in the utensil made of gold from Paradise, سُـبْحٰـنَ الـلّٰــه it was splendour upon splendour.^[2]