Here are some tools you may need:

On a two-handle faucet, try tightening the bonnet shown below. 

If that does not work, you may need to replace the stem.

Purchase Delta Genuine Part RP1740 – For one stem assembly per package, or RP25513 for those requiring the quarter-turn stop.  To replace the stem:

1. Shut off water supply.

2. Cover drain opening so parts won’t fall into it.

3. If you have lever handles, loosen the set screw with an Allen wrench and remove the handle. If you have knob handles, pry off the handle button, remove the screw and lift off the handle.

4. Unscrew bonnet nut. Use a crescent wrench to loosen if necessary.

   

5. Pull stem straight up and out.

   

6. IMPORTANT—STEM MUST BE REPLACED PROPERLY.

   1. Knob handle stem position: Slip the stem unit into the body, aligning the tabs on the stem with the slots in the body, so the “stop” on each stem points toward the spout.

   2. Lever handle stem position: Align the tabs on the stem with the slots in the body, so the “stop” on each stem points toward the right. If you have lever handles, you may also need to reinstall the quarter turn stops to limit the handles from turning more than 90º. Note: If you reinstall the handles and find that they aren’t turning the right direction, rotate the stem 180º and check for proper handle rotation.

   

7. Screw bonnet nut on and hand tighten.

   

8. Replace handle, tighten screw.