Why is it important to change the sanitizing water when it gets dirty or has organic matter like food debris in it?

The water is sanitized so that it can be consumed by people and remains hygienic. When the water gets dirty it has to be cleaned as the consumption of dirty water can lead to many diseases such as Hepatitis.

Moreover, if organic matter is present in a stagnant water this can cause algae to from in the water which again is not suitable for drinking

you would have a std. i hope this .