DES MOINES, Iowa (AP) — Two rivers that supply water to 500,000 people in the Des Moines area show nitrate levels spiking to levels that make it unsafe for some to drink, a concentration experts haven't before seen in the fall that likely stems from especially wet weather in recent months. The utility that supplies Des Moines and most of its suburbs had workers blending river water with other sources to lower the nitrate levels, but the situation may be nearing the point at which the city starts a process that costs about $7,000 a day to remove them. Pregnant women and adults with reduced stomach acidity are advised not to drink water above the EPA limit. For years, environmental groups have called for the state to regulate livestock farms, much as they already do for city wastewater treatment plans, which must have permits that limit release of contaminants into rivers. Significantly reducing nitrogen levels likely requires slowing the flow of water into rivers by setting up wetlands or planting grasses or other cover crops on harvested fields, allowing the plants to retain water and consume excess chemicals.