There are a number of reasons you might want to substitute for the olive oil in your pesto. Here are two of those reasons and how you can do it!You want to make your pesto veganAll you need to make pesto is basil, pine nuts, garlic, and Parmesan cheese. Olive oil is not an essential ingredient, so adding some water instead of olive oil will keep your pesto vegan without altering the taste or consistency too much. Even if your recipe calls for a cup of olive oil, it should be pretty easy to replace that with just under a cup of water.You're out of olive oilYou don't have time to go to the store and restock on olive oil, but you still want that delicious pesto flavor in your life. If this sounds familiar, you can use some water instead of olive oil in a pinch. It won't give pesto exactly the same texture as using olive oil would, but it will still taste fine. Just use less water than you would use olive oil. For example, if your recipe calls for one cup of olive oil, use three-quarters or two-thirds of a cup of water instead.