The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: "Flowing water is not rendered impure by anything that falls into it from creatures with flowing blood that die in it, nor by any impurities, unless the impurity overwhelms it and changes its color, taste, or smell. This only occurs when the water is small in quantity, its flow is weak, and the impurity is abundant." This ruling is supported by the aforementioned verse and narrations, as the term "water" encompasses it. However, the indication that it becomes impermissible to use if altered is also clear.
Commentary #2