Add water, raspberries, and fresh lemon juice to the blender. Blend until smooth.
Strain mixture through a fine mesh strainer to remove seeds (optional but recommended).
Pour into Ninja Creami container and freeze on a level surface for at least 18 hours.
Remove from freezer and run a little warm water along the outer edge for 30 seconds (or leave on the counter for 7-10 minutes to thaw).
Process on the sorbet setting. If needed, respin until you reach your desired texture.
Notes
I recommend straining the raspberry mixture after blending so you don't have a lot of seeds in your sorbet and get a smoother sorbet.
Before processing, I usually run a little warm water on the outer edge for 30 seconds.
If you have leftovers, smooth out the top and return to the freezer. You may need to reprocess before enjoying again or leave on the counter for 10-15 minutes to thaw to make sorbet scoopable.