
Mix the water, vinegar, and sugar until the sugar dissolves. Add the dill weed.
Use a mandoline slicer or kitchen knife to thinly slice the cucumber and red onion to about 1/8 inch thick (about 2 millimeters). Peeling the cucumber is optional.
Add the cucumbers and onions to the water/vinegar mixture. Let them marinate for at least 2 hours or up to 4 days in the refrigerator.