How to make an indoor waterfall?
Most people use metal/stone type structures, like a piece of furniture. It really depends on the effect you are after. If you want it too look like a real pond-type waterfall, consider a heavy duty plastic mold liner from HD or Lowes. Then you can create free form with stones and plants. Put a heavy duty pliable liner underneath for any future leaks that could occur with age (it would move the water outwards to have a visual of a problem) Place the pool in desired location, Add rocks/small boulders around and keep stack up, making sure all is stable. Choose the place where the water will be “tubed” upward and come out, building stones on up in this direction. Use plants and smaller rocks to fill in any places where edge of liner is still visual. As with any water product check for leaks or any problem periodically. It has to be maintained and kept clean. Also keep your pump in accessible place for repair/replacement.
