While my car was in for its 60,000 mile service, they found a leak in the water pump and recommended replacing it.
Was causes a water pump to leak and need to be replaced on 2004 Toyota RAV4
The original Toyota water pump is usually pretty reliable. The water pump on that engine is externally mounted not driven by the timing belt as in previous models so it is a little easier to replace. The labor to replace the pump alone is still about 1.5 hours. An overly tight fan belt or "dirty' engine coolant can contribute to premature water pump wear causing it to leak.
The water pump has a bearing for the impellar and there is a seal on that shaft. When the seal wears out, the coolant leaks past the seal and there you have the leak problem.