1. Use room temperature water
The poinsettia originates from tropical Mexico, so it doesn't like cold water any more than cold air. After filling up a watering can, it’s best to let water sit for a little until it’s reached room temperature.
2. They prefer soft water
Poinsettias don’t like hard water. Rainwater is naturally soft (low in minerals like lime) and is therefore perfect for plants - you can collect it outside to water your poinsettias. In regions with hard drinking water, you could reduce the mineral content of tap water by boiling it or letting it stand for a day. This deposits the minerals that make the water hard. You can also mix tap water with distilled water or use a water filter. Tip: If you use a tumble dryer, you can also use the water from the drying process to dilute water that is too hard.