Local officials warned more than half a million Iowans in the state’s capital city and suburbs on Thursday that near-record level of pollutants in its rivers could make drinking water dangerous if immediate steps are not taken to reduce demand.
But the officials declined to explain what they believe has caused the surge in nitrate levels, which has historically been tied to runoff from farmland draining into Des Moines-area rivers.
The water utility, Central Iowa Water Works, issued a f…