Why is my pregnant dog leaking clear liquid

Probably because her water broke, and her pups are coming ! I hope you are prepared for her and have a clean dry bed so she can have them in comfort.

Tick

If you don't know what you're doing then call a vet. Dogs can die during labor and birth, that's why we (people for the humane treatment of dogs) never recommend backyard breeding.

Call your vet, get her in just to make sure everything goes smoothly.

While you're there, make an appointment to have her spayed.