Mix joint compound with water in the bucket until the joint compound has the consistency of paint.
Pour the joint compound into the paint tray. Load the paint roller with the thinned joint compound.
Check the consistency of the joint compound on a scrap piece of drywall. Run the roller over the drywall and examine the joint compound you applied to the vertical surface. It should adhere with texture, but it should not drip or run down the vertical surface. Adjust the consistency by making it thinner if it drips or making it thicker if it does not roll easily.
Apply the thinned joint compound to the wall with the paint roller in the same way you would apply paint. Cover the entire wall with a thin and even layer of joint compound to make the orange peel texture. Allow the wall to dry for about 10 minutes.
Apply a second coat of joint compound to the wall over the dried first layer. Continue to apply the second layer until you coat the entire wall and you like the effect. Go over any areas with the paint roller before the joint compound dries to adjust the texture. Allow the second coat to dry completely before you paint the wall.