Place the cashews in a small container and add the warm water. (If it doesn't cover the cashews completely, just add more warm water.) Soak for 1 to 4 hours unrefrigerated or up to overnight in the refrigerator.
Drain and rinse the cashews, then place them in a blender or food processor. Add the olive oil, the 1/4 cup water, the lemon juice, and the garlic. Process until smooth and creamy, stopping occasionally to scrape down the sides of the processor, about 5 minutes total. Mix in the chives and add salt and pepper to taste.
If you'd like a lighter texture, add warm water, 1 tablespoon at a time, until you achieve the desired consistency.