Question

choose the correct answer. why is using river water for drinking water a possible problem for cities downstream from other cities? because there may be too many fish and other species in the water because the upstream cities use it all up so the river runs completely dry because treated sewage is pumped back into the river by upstream cities

Explanation:

Upstream cities may pump treated sewage back into the river. Treated sewage can still contain contaminants, pathogens, and chemicals that make the water unsuitable or risky for drinking by downstream cities. The presence of fish is not a direct drinking - water problem. And while water over - use by upstream cities can be an issue, it's less common for a river to run completely dry due to city water use alone compared to sewage discharge.

Answer:

because treated sewage is pumped back into the river by upstream cities