Tirmidhi

Benefits and Issues:
➊
If a straw or something similar falls into the water, it should be removed with something (such as a spoon, etc.), or a little water should be poured out so that the straw comes out.

➋
If milk or tea, etc., is hot, one should also avoid blowing on it to cool it down. Instead, pour it little by little into another vessel and drink it.

➌
Some scholars have derived from this that for a sick person, one should not recite any surah or supplication and blow into the water, but rather perform the blowing (ruqyah) directly on the patient and supplicate, because both of these actions are Sunnah, whereas blowing into water is not Sunnah.
And according to some scholars, blowing into water is permissible, because in ruqyah, Surah al-Fatihah and supplications, etc., are recited. In order to transfer their effects into the water, there is no alternative but to blow into the water; therefore, according to them, blowing into water for ruqyah is different from ordinary blowing. In normal circumstances, blowing is certainly prohibited, but blowing for ruqyah is permissible.
And Allah knows best. (See the article: "Is it not permissible to perform ruqyah on water?" by Hafiz Salahuddin Yusuf, published in Al-I'tisam, vol. 55, issue 30, 1 August 2003, and Fatawa ad-Din al-Khalis (Arabic), Mawlana Aminullah Peshawari, vol. 5, pp. 40–44)