Why have water uses been categorized, and why is the use of water mentioned in customs but not in acts of worship?

When discussing acts of worship and daily customs, jurists divide water into three categories: ṭahūr (pure and purifying), ṭāhir (pure but not purifying), and najis (impure). Ṭahūr water is used for removing ritual impurity (rafʿ al-ḥadath) or purifying from physical filth (ṭahārat al-khabath) (acts of worship), and it is also suitable for daily customs like cleaning, drinking, and eating. Ṭāhir water, on the other hand, is only suitable for daily customs, whereas najis water is neither suitable for acts of worship nor for daily customs.