Why is protected water usually safer to drink than unprotected water from wells or rivers

Why does a tidal bulge occurs on opposote sides of earth

Geologists know that potassium-40 decays to argon-40, with a half-life of 1.3 billion years. if an analysis of a feldspar crystal in a sample of granite shows that 75 percent of the potassium-40 atoms have decayed to form argon-40, what is the age of the granite

Advantages and disadvantages of mitigation and adaptation