I always use rain water.
ChatGPT (planty) says this about tap water:
Pros: Readily available and usually safe for most plants.
Tips: Let the tap water sit out for 24 hours before use. This allows chlorine to evaporate, which can be harmful to delicate cuttings.
Watch Out: Some areas have hard water or high fluoride levels, which can affect plant health over time.
Pros: Naturally soft and full of nutrients that encourage root growth.
Collection Tip: Use a clean container to catch rain and store it in a cool, shaded spot. Avoid water that might have contaminants from dirty roofs or gutters.