Use the olive oil and cook the onion and garlic until they soften. Pour in the passata and let it simmer for 2min.

Then add the water and orzo pasta. Let it cook on a medium heat for 20min. Stir it frequently so it doesn't stick to the bottom of the pan.

After the 20min take it off the heat. Season with salt and pepper and stir it well. Cover the pot with a clean towel and the lid. Allow it to stand for 10min at least. I sometimes let it on the stove for 30min if i have the time so that the sauce is absorbed.