Is it also OK to put "the" in front of "public health"?
If so, how should I understand the usage of "the" in this context?
THanks
It would be unnatural. "Public health" is usually uncountable and so doesn't attract an article.
If you wanted to use "the" you would say "...utilising water and threatening the health of the public." However, "...threatening public health" sounds much better.
For info, it would be "raising (not rising) the cost of using water".