Answer: the hydrosphere and the biosphere
The hydrosphere is the sphere which includes different regions occupied with water these includes oceans, lakes, ponds, rivers and even the water that seep inside the soil and rocks retain in the form of aquifiers and groundwater. The biosphere is the region of earth that is occupied with various life forms like flora and fauna.
In the given situation, the available water for the plant growth in a rainforest is because of retention of rainwater in the grounds as aquifiers or groundwater utilized by plants for growth. These plants are the part of the earth's biosphere.