sources — any thing or place from which something comes, arises, or is obtained; origin: Which foods are sources of calcium?
reservoirs — a small body of standing water; pond.
causes — a person or thing that acts, happens, or exists in such a way that some specific thing happens as a result; the producer of an effect: You have been the cause of much anxiety. What was the cause of the accident?
roots — a part of the body of a plant that develops, typically, from the radicle and grows downward into the soil, anchoring the plant and absorbing nutriment and moisture.
wells — a hole drilled or bored into the earth to obtain water, petroleum, natural gas, brine, or sulfur.
