We have a gravity feed purifier with filter “candles”. It works great, but the candles always get stopped up in winter and a new set costs upward of $170. We use the water primarily for drinking and keeping my wife’s marine aquarium topped off. We purchased a Model PD three weeks ago and, WOW!, is it an amazing unit. Because no more candles need bought, this unit is going to save us a ton of money and it is a real workhorse. We are very pleased with not only the performance, but the design and construction are top shelf, too. Great design and so easy to operate.