Make the manually poster with water drop falling in Photoshop. Source link: http://www.photoshophelps.com/2016/03/28/poster-on-save-water-save-life-photoshop-tutorial/
If you want a banner on a water topic easily and fast. Just go to photoshop and do easy step with best tools like brushes etc. Link: http://www.photoshophelps.com/2016/03/29/photoshop-tutorial-to-make-easy-poster-on-save-water/
If you have event in public place of water consumption. and you have need a water poster for wonderful event. Do your own with Photoshop using some wonderful tools. Make new file, apply artfully on the poster.