We had a small hand pump toy that would suck up the tub water and spray it. It was a manual pump so it taught cause/effect which is critical for development.

Second the swimming lessons. I have two daughters with a rare genetic condition and they are obsessed with swimming in the pool. My older is physically challenged, wears AFO legs braces, has a seriously disturbed gait, and frequently uses a chair when we’re out in public. But she can swim non-stop for an hour. Great exercise, great strength building, great for safety. I feel like her freedom in the water is an escape from her limitations on land. :D