Yes, we need to reuse water, ...

Yes, we need to reuse water, we often CAN get away with it. However, our ignorance is still very great, risks abound, and we always need to reduce our ignorance. Fortunately, ignorance can be fixed.... with enough new knowledge to gradually identify and reduce the harm. On the other hand, you can't fix "stupid' as easily. Science is the key, and is always increasing, always needed, and is essentially never done. We, far too often, assume 'safety' when we are short-cutting the science. When we take scientific shortcuts, we always need to acknowledge our ignorance, try to decrease it, and fear our hidden stupidity.