There are many reports of growers having better cannabis crops when they use distilled or purified water.
This is likely true because tap water can have all kinds of heavy metal in it.
You can get rust, lead, sodium and calcium from the hot water tap. The cold water tap will have less sodium and calcium, and it’s a good idea to run the water for a little while to avoid too much sediment. You’ll find that if you get too much alkaline salt buildup in your soil, your plants might experience a lockout of nutrients which can cause iron, copper, and zinc deficiencies. You certainly don’t want to run into serious problems like that, so using distilled water is not a bad idea. You can always get a water distiller and make as much distilled water as you need. You can also use a charcoal filter to get rid of a lot of the nasty stuff found in hard water, but it will still have some undesirable things such as sodium and various heavy metals. Even when using your regular fertilizers, you will want to flush out your potting mediums every so often with water to make sure you don’t have too much buildup of different types of salts. You don’t want your cannabis plants to develop a nutrient lockout, so those flushes with regular water or distilled water can help a great deal to prevent that from happening. Also when you are watering your cannabis plants, you should have the water between 70 and 80 degrees fahrenheit, so that you don’t cause shock to your cannabis plants.