I filled the bottle with water until the first mark. I cut out a black cardboard exactly the size of the bottle and I placed behind it. The waterfall is an old photo of mine. I should have used a glass bottle instead a plastic one and with no scratches. You can take this type of photos at the waterfall location. The light and better, you can use low ISO to avoid the noise, as in this photo. The only problem are the curious who come to ask you what you're doing, to give you absurd advice, and make you weird questions about your equipment. :)
