Firstly: Categories of Water
Scholars have differed in categorising water according to many opinions, the strongest of which are two:
The first: that water is of three types:
- Purifying (tahur)  Al-Qurtubi said: "The Ummah is in agreement by consensus that both legally and linguistically the term 'tahur' may refer solely to water and not to other liquids which are pure. The scholars reserving that term for water is the clearest of proofs that 'tahur' is also that which is 'mutahhir' (purifying)." Al-Jami` li-Ahkam al-Qur'an (13/41)
- Pure (tahir)
- Impure (najis)
This is by agreement of the four schools of jurisprudence generally.  They differ within these types, whether some types of water would fall under pure or purifying.
The second: that water is of two types only: purifying and filthy. This opinion is narrated from some Hanafis, and it is what Ibn Taymiyyah, Ibn Baz, and Ibn `Uthaymin chose.
Secondly: Plain Water
1. Defining plain water
Unconditional water: is water that has remained upon its original nature.
2. Types of plain water
● River water
● Well water
● Snow  There is no difference among the scholars about using snow for purification after it has melted. They differ over its usage before melting, however. and hail  Barad in Arabic is stone-like frozen pieces of water that fall from clouds. falling from the sky
● Spring water, which is what stems from underground
● Zamzam water
- The ruling of using Zamzam water for purification:
It is permissible to perform ablution as well as ritual washing with Zamzam water, and this is by agreement of the four schools of jurisprudence.
- The ruling of using zamzam water for removing najas:
It is sufficient to use Zamzam water to remove najas, and this is by agreement of the four schools of jurisprudence.
- The ruling of sun-heated water:
It is permissible to use sun-heated water  Like using solar power to heat up water. for purification with no dislike, and this is the Hanbali opinion. It is also the Zahiri opinion, one of two opinions among the Malikis, one position among the Shafi`is, and the choice of al-Nawawi, Ibn Taymiyyah, Ibn al-Qayyim, and the verdict (fatwa) of the Permanent Committee.  The Permanent Committee for Scholarly Research and Ifta, Saudi Arabia
- Water heated by a pure substance:
It is sufficient to use water that has been heated by a pure substance. Ibn Taymiyyah quotes a scholarly consensus on the matter.
- Water heated by a najis substance:
If water is heated with a substance that is najis but nothing reaches it from the najasah such that it is adulterated, then it remains upon its original state of purity. Ibn Taymiyyah quotes a scholarly consensus on the matter.
- Purification using haram  Haram is one of the five Islamic legal rulings, and it means that the matter in question is prohibited as well as sinful if committed, so legally impermissible. water:
Purification is valid if performed with haram water (like that which has been forced away from its owner or stolen) but is nonetheless sinful. This is the opinion of the majority: Hanafis, Malikis, and Shafi`is.
Thirdly: Najis Water
1. Defining najis water
Najis water: is that water which has been adulterated by najasah, such that its colour, scent, or taste changes.
2. The ruling of najis water
It is not permissible to use najis water for purification. Ibn al-Mundhir and Ibn Nujaim both quote scholarly consensus on the matter.
Fourthly: Water that is mixed with other substances or has denatured.
1. If water denatures due to a najis substance
If water meets a najis substance such that it changes one of its properties; that is, its taste, colour, or scent have been changed, then the water is thence classified as najis, regardless if it is a lot of water or a little. Consensus  A view is attributed to `Abd al-Malik ibn al-Majushun that water’s scent changing does not affect its purity, but this is a Shadh (strange and anomalous) view. on the matter has been quoted by: al-Shafi`i, Ibn al-Mundhir, Ibn `Abd al-Barr, Ibn Qudamah, and Ibn Taymiyyah.
2. If plenty of water meets a najis substance
If the water is plentiful and mustabhir,  Mustabhir here refers to wide expansive spread of water. then it does not become najas due to changing its properties. Consensus has been quoted on this matter by: Ibn Jarir, Ibn al-Mundhir, Ibn Hazm, Ibn `Abd al-Barr, Ibn Rushd, Shams ud-Deen Ibn Qudamah, and Ibn Taymiyyah.
3. If a najis substance falls in flowing water
If the water is flowing  Flowing water is what is considered by people to be flowing, though there are other views in terms of how to categorise it. and a najis substance falls in, then the water does not become najis except if it changes its properties. This is the opinion of the Hanafis and Malikis. It is an old opinion held by al-Shafi`i which is still held by some Shafi`is. It is also the more correct of two reports from Ahmad, as well as being the chosen pinion of Ibn Qudamah and Ibn Taymiyyah.
4. If scarce water meets a najis substance but does not change
If a little amount of water meets a najis substance but does not change its properties then it does not become najis itself. This is the opinion of the Malikis, Zahiris, the opinion of a group from the Salaf,  Literally means bygone, but refers Islamically to the early Muslim generations, usually the first three – the companions of the Prophet ﷺ, their followers, and the followers of their followers. The first two generations will henceforth be referred to as the Companions and the Followers respectively. a narration from Ahmad chosen by a number of Hanbalis, the opinion of Ibn al-Mundhir, al-Ghazzali, more than one from the Shafi`is, Ibn Taymiyyah, al-Shawkani, al-San`ani, Ibn Baz, and Ibn `Uthaymin.
5. Water that has been changed with proximity to a najasah
If water changes its scent due to its proximity to najasah, then this does not take away from its purity. The majority have stated this explicitly: Malikis, Shafi`is, and Hanbalis.
6. Purifying najis water
Whenever the change in nature of najis water disappears by any means,  There are many ways for a najasah to be removed. Among those are: that the water naturally purifies itself, or through the addition of some soil or extra water, or by draining some of it. Scholars have detailed conditions and constraints for the fulfilment of each water purification method. even by modern means,  As takes place in some modern factories in converting streaming water to drinkable water, through chemical treatment and sterilisation, whether through electrolytic deposition, aeration, or the use of chlorine. Those who hold this view have placed as a strict condition the complete and total purification of the water such that it returns to its original, natural state, without a sign of the najasah, be it smelt, tasted, or seen in colour. Primary, secondary, or partial distillation processes do not suffice if any trace of said najasah remains. They also preferred avoiding such water when it comes to drinking when possible. This is mainly out of precautionary principles, like preserving one’s health and deterring any harm potentially incurred by this type of chemical process, as well as out of principle, preserving one’s nature from what one would naturally be disgusted and put off by. then it has been purified, and there is no difference in this between the plentiful and the scarce. This is the position of Malik in general, the chosen opinion of Ibn Hazm, al-Shawkani, Ibn Baz, Ibn `Uthaymin, and to its accordance the position of the Islamic Fiqh Council of the Muslim World League.
7. Water that is mixed with an insoluble pure substance
If water has been changed due to fat, pieces of camphor, ambergris, or any other substance that is not soluble in water nor breaks up in it, then the water is purifying. This is the position of the majority: Hanafis, Shafi`is, and Hanbalis, and it is an opinion among Malikis.
8. Water denatured due to mixing with a pure substance that is difficult to keep it away from
If water denatures due to a pure substance that is difficult to keep it away from,  Like water which denatures due to weeds which grow in it, or tree leaves which fall on it, or that water which denatures due to something that cannot be separated from its resting or streaming place, or denaturing which takes place due to what its stream carries of twigs and chaff. As well as this, it is water which denatures due to its container if it be from leather or copper, and a modern pretext now is water flowing in waterpipes and taps. then the water is still purifying. This the overall view.  A shadh difference of opinion is attributed to Ibn Sirin regarding brackish water. Consensus has been quoted in the matter by Ibn Rushd, Ibn Qudamah, and Ibn Taymiyyah.
9. Water denatured due to its prolonged stillness
Water that has denatured due to stagnation  Brackish water whose colour and taste has changed due to prolonged stillness. is purifying by agreement of the four schools of jurisprudence.
10. Water denatured due to salt
Salt does not take away from water remaining as purifying. This is the position of the Hanafis,  Though they distinguish between water which is salty by nature and water that is artificially saline. The former is upon its original state, while the later has had its original state altered. Also, the differentiation is due to it solidifying in summer and dissolving in winter – the opposite of normal water. Malikis, a group of the Shafi`is, an opinion among the Hanbalis, and it is chosen by Ibn Taymiyyah, Ibn Baz, and Ibn `Uthaymin.
11. The ruling of using Nabidh for purification
Purification with Nabidh is invalid,  Nabidh is the juice taken from dates or raisins, then left in a vessel with water added to it. If it is left until it foams, it becomes intoxicating. Any modern drink with similar properties would take the same ruling by analogy. regardless whether there is an availability of water or there isn't. This the position of the majority: Malikis, Shafi`is, Hanbalis, Zahiris, a narration from Abu Hanifah chosen by Abu Yusuf and al-Tahawi, and it is the position of a group from the Salaf.
Fifthly: Used Water
1. Water  Used water refers to water that drips or falls from the body after it has been used for ablution or ritual washing. used for removing hadath
Water used to remove a state of hadath for ablution or ritual washing is pure in and of itself as well as purifying.  Like water in pools in ponds, it is not makruh to purify oneself from its water, even if some used water falls back into it. This is the position of the Malikis,  Despite viewing it as purifying, Malikis disliked using it for purification if it is little and other than it is available. Zahiris, an opinion among the Hanafis, an opinion among the Shafi`is, a narration from Ahmad, the opinion of a group of the Salaf, the choice of Ibn al-Mundhir, Ibn Taymiyyah, Ibn Baz, al-Albani, and Ibn `Uthaymin.
2. Water used for a mustahabb  Mustahabb is one of the five Islamic legal rulings, and it means that the matter in question is not a must but is rewarding if committed, so legally recommended. act of purification
Water used for a mustahabb act of worship – like renewing ablution – is purifying. This is the position of the majority: Malikis, the more accurate opinion among the Shafi`is, Hanbalis, Zahiris, and Zufar from the Hanafis.
3. Water used for cooling and general cleanliness
Water used for cooling and general cleanliness is purifying. This the position of the majority: Malikis, Shafi`is, Hanbalis, Zahiris, and it is the position held by Zufar and Muhammad Ibn al-Hasan among the Hanafis.
4. Water used for dipping one's hand in after waking
Water used for dipping one's hand in after waking is purifying.  As for the prohibition of one who has just woken from sleep to dip his hand in the washing vessel, then this may be to potential najasah. If this is the case, then it does not remove certainty in the water’s purifying nature. If the prohibition is solely for worshipful purposes however, then one suffices oneself with the textual evidence, and that is the legality of ritual washing. This is the position of the majority: Hanafis, Malikis, Shafi`is, and a narration from Ahmad.
5. Water used to remove najasah and one of its properties changes
Water that has been used to remove some najasah and, due to this, one of its properties changes, is considered to be najas. Consensus has been quoted over this matter by: al-Nawawi, Ibn Qudamah, and al-`Iraqi.
6. Water used to remove najasah and none of its properties change
Water that has been used to remove some najasah and, despite this, none of its properties change, is considered to be purifying. This is the position of the Malikis, an opinion among the Shafi`is, the verdict given by some of the Salaf, and the position held by Ibn Taymiyyah, Ibn al-Qayyim, and Ibn `Uthaymin.
7. The ruling of using a man's excess water for purification
It is permissible to purify oneself with a man's excess  Excess here refers to water left after purification is complete. water, and this is by agreement of the four school of jurisprudence.
8. The ruling of using a woman's surplus water for purification
It is permissible for a man to purify himself with a woman's surplus water. This is the position of the majority: Hanafis, Malikis, Shafi`is according to the most correct opinion, a narration among the Hanbalis chosen by Ibn `Aqeel, and it is also the choice of Ibn al-Mundhir and the position of scholars generally on the matter.
9. A man and his wife performing ritual washing from a single vessel
It is permissible for a man and his wife to perform ritual washing from a single vessel, and this is by agreement of the four schools of jurisprudence, as well as being the choice of the Zahiri Ibn Hazm.