What is the ruling on purifying one's feet and shoes upon entering the mosque or home after walking through wet or dry land that had been submerged by sewage water?

Sewer water is often impure and renders impure the places it submerges. Whatever transfers from it to the feet or clothes becomes impure if it is wet. However, if it is dry, it does not render impure that which it transfers to unless the limb is also wet. Dry parts must be removed without washing, while wet parts must be washed.