I use refillable 5-gallon blue jugs. That's the cheapest route. I have two of them, and it takes $1.90 to fill one. 5 gallons of pure clean water for $1.90 is cheap if you ask me. Definitely worth it when you consider that it saves you the hassle of ever cleaning buildup on your plants, cage, mist nozzles, or anything really. Definitely worth the cost.