The health ministry has instructed water purification plants nationwide to temporarily stop taking in rainwater to prevent tap water being contaminated from radiation leaking from the crippled Fukushima No. 1 nuclear plant, ministry officials said Sunday.

While calling on the plants to keep tap water supplies stable, the Health, Labor and Welfare Ministry also proposed covering the water pools at the plants with tarps to keep rainwater out or using powdered activated carbon to help get rid of radioactive materials. The instruction came after abnormal radiation levels were found in tap water at multiple purification plants in Fukushima, Tokyo and other prefectures.

Radioactive materials sent into the atmosphere by the crisis-hit power plant apparently fell to Earth with the rain. When the rain stops, radiation levels in water tend to fall over time.