Mary,
The water falls and stream are breaking up each gallon of water and increasing it's surface area. The increased surface area accelerates the water evaporation.

This is how commercial cooling towers work for large air conditioning systems. They pump the condenser water to the top of a tower where it is distributed using spray nozzles or a large plate with holes in it. This spreads the water out and it cascades down over "fill' material that used to be made of wood, but is now made of PVC plastic. This further increases the surface area of each droplet of water and aids in the evaporation rate. This evaporation causes adiabatic cooling of the remaining water in the system. Every pound of water that evaporates takes 970 BTU's of heat with it.

Absolutely nothing to do with your question, but might give some insight into where the water is going! LOL

Hopefully this is all there is to it and things return to normal soon!