Thoroughly rinse cucumbers. Remove stems and cut off slice from each blossom end. Pack cucumbers loosely into hot, sterilized quart jar, leaving 1/2-inch headspace. Add dill and mustard seed. Make brine by combining water, vinegar, and salt. Bring to boiling.
Pour hot brine over cucumbers, leaving 1/2-inch headspace. Adjust lid. Process in boiling water canner for 15 minutes. Let stand 1 week before opening. Makes 1 quart.
Kosher-Style Dill Pickles: Prepare as above, except substitute 2 cloves garlic, halved, for the mustard seed.