Pour the water into a pot or any other container and bring it to a boil. Make sure you don't use an aluminum container as the process requires heating for long, and the metal is neither a perfect absorber nor a reflector of heat.
Add Reishi and let it boil for another half an hour. If you prefer a strong flavor, you may let it boil for longer, but keep adding more water as it evaporates.
Turn off the heat and let the mushrooms steep in it for another 30 minutes, even longer if possible. Reishi mushroom is woody, therefore it needs time to steep.
Now you may add optional honey to taste and stir it well.
Strain the mixture into a jar using a strainer or a cheesecloth.
Drink hot, or store in refrigerator in a sealed jar to enjoy cold.