Assalamualaikum ustaz. What is the ruling of water that has been licked by a cat? Hope for an explanation.
Waalaikumussalam wrt. wbt.,
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
We start with Allah SWT’s statement:
إِنَّ اللَّـهَ يَأْمُرُ بِالْعَدْلِ وَالْإِحْسَانِ وَإِيتَاءِ ذِي الْقُرْبَىٰ وَيَنْهَىٰ عَنِ الْفَحْشَاءِ وَالْمُنكَرِ وَالْبَغْيِ ۚ يَعِظُكُمْ لَعَلَّكُمْ تَذَكَّرُونَ
“Indeed, Allah orders justice and good conduct and giving to relatives and forbids immorality and bad conduct and oppression. He admonishes you that perhaps you will be reminded.” 
Al-Sa’di stated that being fair is obligatory, while ihsan (doing good) is an additional value that is sunnah such as a person being beneficial by donating his wealth or body or knowledge or other beneficial matters which include in it (the commandment) to do good to farm animals that can be eaten or others (not eaten). 
Definition of cat
A cat is a small animal with soft and thick fur, kept as a pet and usually catches the mouse.  In the World Encyclopaedia it is stated that cats are a favourite pet for people worldwide. Cats are generally intelligent and independent. This small animal love to play and be entertained. Most cats are kept as loving, loyal companions for humans of all ages. The word cat refers to a family of carnivores which included lions, tigers, leopards and panthers. This family also includes domesticated cats – that is, cats that are defended as pets.
Cats vary in character and certain physical characteristics, such as the length and color of their fur. There are many breeds of cats. Special features distinguish each breed from other breeds. Among the favorite breeds are Siamese cats, Burmese cats and Persian cats. No one knows exactly when cats began to be domesticated. But some authorities believe that cats were domesticated about 5000 years ago. Throughout history, humans have valued cats for their skills in hunting and killing mice, rats and snakes. Cats help keep farms, homes, and businesses free of these pests. 
Cat is a pure animal
Cats are pure and usually roam amongst people. Kabsyah binti Ka’ab bin Malik reported, one day when Abu Qatadah was at home, he prepared a container filled with water for ablution. Then, a cat came and drinks the water. Abu Qatadah just let the cat drink from the container. Abu Qatadah then realizes that Kabsyah was watching him all along, then he asked: “Are you confused, my nephew?” Kabsyah answered: “Yes.” Then Abu Qatadah explained that Rasullullah PBUH once said:
إِنَّهَا لَيْسَتْ بِنَجَسٍ، إِنَّمَا هِيَ مِنَ الطَّوَّافِينَ عَلَيْكُمْ، أَوِ الطَّوَّافَاتِ
“It is not unclean, but is one of those who intermingle with you.” 
Thus, we learn here that there is a relaxation and special ruling given for cats for they are included as animals that are usually found intermingling with people and kept as pets.
Al-San’ani stated in his book that Allah SWT has granted facilitation for His slaves (regarding the rulings related to cats) by making it pure and not najis to ease the burdens of people and this hadith is the evidence that cats are pure and also the container (from which the water is drunk). 
There is a narration from Aisyah R.Anha, from the Prophet PBUH that the Prophet PBUH puts a container close to a cat for it to drink. Then the Prophet PBUH performed ablution using the remaining water in the container.  al-Syaukani stated that there is a difference in opinion among scholars on this hadith from ‘Abd Rabbih which is Abdullah bin Sa’id al-Maqburi. Furthermore, al-Daraqutni also narrated this hadith from Aisyah through another route of which there is a narrator named Bernama al-Waqidi. Likewise, it is narrated from other narrations where all of them there are doubts in them.
This hadith shows the purity of the cat’s mouth and the remaining water it drank from. This is the opinion held by al-Syafi’I and al-Hadi. While in Abu Hanifah’s opinion, it is najis just like other wild animals. However, there is rukhsah (facilitation) on it, where the remaining water from which a cat has drunk from is makruh – to be used,  and it is not makruh to use it if there is no other available water. 
However, in madhhab al-Syafi’I, the remaining water from which a cat has drunk is pure and it is not makruh to use it.  Ibn QUdamah also stated that for any animal its leather (coat), fur, sweat, tears or saliva follows the ruling of the container (of which it has drunk from) whether it is pure or najis. 
According to the above discussion, in our opinion the remaining water from which a cat has licked or drunk is pure and it is not makruh to be used. Especially for cats kept as pets and mingle with humans.
May Allah SWT grant us all a clear understanding in practising this religion. Amin.
 See https://prpm.dbp.gov.my/cari1?keyword=kucing. Diakses pada 30 Disember 2021.