You can fill your olla as soon as there is little or no water left inside the container. At the beginning of use, you fill it once a week. After several weeks of use, you will see if your plant needs a lot of water (the olla empties quickly) or if it does not need much water (the water will stay in the olla longer). The olla will adapt the water diffusion to the needs of your plant. Filling requirements will therefore change (every week, every fortnight, etc.). If there is still water in the container, you do not need to add any more.