Explanation of the hadith
The Messenger of Allah (may Allah's peace and blessings be upon him) clarified that pure water does not become impure once impure things are thrown in it, as long as its color, taste or smell do not change.
Water is pure and nothing makes it impure
Authentic hadithAn-Nasaa’i - Narrated by Abu Daoud - Narrated by AhmadHadeethEnc #8356
عن أبي سعيد الخدري رضي الله عنه أنه قيل لرسول الله صلى الله عليه وسلم : أنتوضأ من بِئر بُضَاعَةَ وهي بئر يُطرحُ فيها الحَيضُ ولحم الكلاب والنَّتَنُ؟ فقال رسول الله صلى الله عليه وسلم : «الماء طهور لا ينجسه شيء».
English translation
Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) was asked: "Can we perform ablution from the well of Budā‘ah, which is a well into which menstrual pads, dead dogs and stinky things are thrown?" He replied: "Water is pure and nothing makes it impure."
Rulings of Water