Designs for an adjustable cat fountain that uses a small water pump. The design was made for a enamel bowl but can be adjusted for any bowl by editing the .scad code in OpenSCAD. If you don't wish to downlaod OpenSCAD the parts can be customized here: https://www.thingiverse.com/thing:4047026. The completed print in clear PP is of the Cat_fountain_3.stl. The print ran out of filament while printing the pump tube but the part still worked. After the part was edited to further minimize material use and the Cat_fountain_angle_channel.stl was generated in OpenSCAD. The varios .scad file variants have different channel geometries.
Parts used and price
A cat fountain that fits any bowl and has a filter was already designed (https://www.thingiverse.com/thing:2861327/files) but was not adjustable. The flowing water area was also not near the level of the bowl's water to allow easy drinking access. My cat also didn't mind drinking out of a fake stone fountain that didn't have a filter before it broke so I didn't find the filter to be nessary.