Ibn Majah

Commentary:
(1)
Islam, in its teachings, has also taken into consideration the principles of hygiene. An example of this is the blessed hadith in which there is a command to cover food and drink items in order to protect them from harmful things.

(2)
Harmful substances such as dust and the like can very quickly mix with water. When the quantity of water is small, as is the case in household vessels, even a little contamination can render the water unusable. The wisdom in tying the mouth of a water-skin is that in this way the water is protected from contamination and there is no fear of it becoming spoiled.

(3)
Whether the vessels are for water or for food, one should certainly place a lid or cover over them so that dust and insects cannot enter, because some insects can also be dangerous. Especially at night, small insects come out of their holes and can enter food and drink items; therefore, there is a particular command to cover vessels at night. See: (Sahih al-Bukhari, al-Ashriba, Chapter: Covering the Vessel, Hadith: 5623)