You could install a koi pond, which is a pond designed to house koi fish. Koi ponds can be as small as 10 square feet or less, and they can be installed in indoor or outdoor spaces. Another option is to install a water garden, which is a small garden that features a water feature such as a fountain or pond. Water gardens typically range in size from 2 to 3 feet wide by 4 to 5 feet long, and they can be installed indoors or outdoors.

If you're looking for something smaller than a pond, you might want to consider a fountain or waterfall. Fountains come in all shapes and sizes, and many of them are quite affordable. You can even buy portable fountains that you can set up in your garden or on your patio. Waterfalls are a bit bigger than fountains, but they still don't require as much space as a pond. And if you have some extra room in your garden, a waterfall can be the perfect way to add some extra visual interest.