Is purification permissible from a tank in which a dead mouse has fallen?

If a dead mouse falls into a tank of water, the ruling depends on three scenarios:

1. Water changes: If the color, smell, or taste of the water changes due to the mouse, then it becomes impure (najis) and ablution (wudu') with it is not valid, regardless of whether the water is little or much. This is a matter of scholarly consensus. 2. Water does not change and is more than two qullatayn: If the water does not change and its volume is not less than two qullatayn (approximately 500 Iraqi ritls), then it remains pure and ablution with it is valid, based on the hadith (definition): "If the water reaches two qullatayn, it does not become impure." 3. Water is less than two qullatayn: If the water is less than two qullatayn, it becomes impure simply by the dead mouse falling into it, whether it changes or not. This is the view of the majority of scholars and is the more cautious opinion (al-ahwat (definition) al-mufta bihi). However, the Malikis and Ibn Taymiyyah hold that it does not become impure unless it changes.