Bring water to a boil in a steamer pan. Arrange the asparagus on the steamer rack, place over the boiling water, cover, and steam until tender-crisp, about 4 minutes. Remove the asparagus from the steamer and let cool completely. Cut the spears in half on the diagonal.
Slice the radishes thinly crosswise, cut lengthwise into quarters, or leave whole, depending on their size. Peel the ca