Why is underground water cold?

Answer: Earth insulates from surface heat

Earth insulates from surface heat ✓ — Correct! Underground water maintains a relatively constant temperature close to the average annual surface temperature of that location (usually 10-15°C). The earth acts as insulation, protecting groundwater from daily and seasonal temperature swings. This is why caves feel cool in summer and warm in winter! However, water gets warmer deeper down due to geothermal heat from Earth's interior.

Rocks cool the water — Wrong. Rocks don't actively cool water. Rocks act as insulators, maintaining water at a stable temperature. The coolness comes from being insulated from surface heat variations. At shallow depths, groundwater temperature reflects the average annual temperature of the region.

Lack of sunlight makes it cold — Wrong. Lack of sunlight doesn't directly make water cold - it just means no direct heating. Underground water is cool because earth insulates it from surface temperature changes. The stable temperature is close to the annual average surface temperature. Deep underground, water actually gets warmer from geothermal heat!