Why is there a large amount of water on the ground around my heat pump compressor?

It is from the heat pump defrosting. It is normal for water to be around a heat pump when it is in the heat mode during winter. Many times the water will freeze before it evaporates.

Probably just defrosting. As the heat pump draws heat from the outside air, ice forms on the inside of the coils even though it is above freezing (this can happen all the way up to 38° or 40°F). There is a small timer in the outdoor unit that senses if there are freezing conditions, and after the appropriate time, reverses the valve to pump heat back to the outdoor coil and thaw it. The result is a puddle of water at the base of the unit every hour or so when the conditions are just right.