this is a source image of this week and its called sicily

opened this image and using ctrl + t resized. then used layer mask and starte to give the form.

now decided to make it look like the water is falling from the pavement to the cave. so, choose this waterfall.

to extract the water, press image + adjustment+ desaturate. to give black and white tone. again press image+adjustment+ levels. that will give more contrastat.

now go to channels and i choose the red channel because it has more contrast. then duplicated this channel, and to the new channel press image+adjustment+curves. and try to make whiter. now on this channel press ctrl+click, and this will make a selection of the white parts.
now press the eye icon of the rgb channel and press ctrl+ c to copy. now go to layers and create a new layer and press+v to paste.
now you have only your water selected. paste it to your image and mask it until you get what you want.