The best water to use for houseplant propagation is clean, distilled, or filtered water. Tap water can contain high levels of minerals, chlorine, and other chemicals that can harm or hinder the growth of the cutting or the new plant. Here are some options for the best water to use for houseplant propagation:

1. Clean water: Clean water that is free from contaminants is always the best option for houseplant propagation. If you have access to a clean, natural water source such as a spring or well, this can be an ideal option. However, it's important to make sure that the water is free from pollutants, bacteria, and other contaminants.

2. Distilled water: Distilled water is a good choice for houseplant propagation because it has had all impurities removed through a distillation process. This means that it is free from minerals, chlorine, and other chemicals that can harm or hinder the growth of the cutting or the new plant.

3. Filtered water: If you don't have access to clean or distilled water, you can use filtered water for houseplant propagation. Filtered water can remove some of the impurities that are present in tap water, such as chlorine and minerals. However, it's important to make sure that the filter is effective and that the water is safe for your plants.

4. Boiled water: Boiling tap water can remove chlorine and other chemicals that can be harmful to your plants. However, boiling does not remove minerals, so it may not be the best option for plants that are sensitive to mineral buildup.

In summary, the best water to use for houseplant propagation is clean, distilled, or filtered water. Tap water should be avoided if possible, as it can contain high levels of minerals, chlorine, and other chemicals that can harm or hinder the growth of the cutting or the new plant. Using the right water for your plants can help them thrive and grow strong and healthy.