I've had RO systems for the better part of 20+ years. Our household goes through a lot of fresh water daily, so having an RO system has paid for itself many times over. Even if you don't go through a ton of water for drinking, cooking, iced tea, etc...the convenience of not having to buy unlimited amounts of bottled water and/or filling water jugs at your local water store is definitely an added bonus. I've had 3, 4 & 5 stage RO units throughout the years and they've all produced great tasting water. My past 3 or 4 RO units (which are usually purchased when we move houses) have been Watts Premier models. They specialize is very fast & easy filter changes and they are definitely easy filter changes. However, you pay a little larger price for that convenience. Their 4-stage RO units run about $200 and the yearly filter changes run about $60. RO units also have 2 types of faucets: 1) faucets with an air-gap and 2) faucets without an air-gap. By definition: "Air gap faucets were designed to protect the RO system. In the event of clogging, a small amount of air, rather than dirty water, would go back into the RO system". The air gap will always make some noise when the tank is filling as air and water pass through the drain line and sound escapes from the little air gap hole. The Watts Premier RO systems have an air gap. If your system has an air gap, you cannot replace the RO faucet with a non-air gap faucet...you need to replace the faucets (if necessary) with the same kind. During my most recent search for an RO unit to install in a new home purchase, I came across this Express Water RO unit at an amazing price (which included a year of filter changes). I was a bit skeptical given the price, but the amount of solid reviews made it an appealing option. I made the purchase and had friend help with the install since I am a large framed man that does not easily fit under the sink area. After a month of use, I can say I am very happy with the taste, performance & overall experience with the RO. With that said, I found myself missing the benefits of the permeate pump that I had installed in my last house. If you just care about the RO review, then I am very pleased and give it 5 stars. If you want to know what a permeate pump is and WHY you should get one, read on. This is the permeate pump available on Amazon that I purchased and am reviewing below: https://www.amazon.com/gp/product/B005VPPRX4/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1 Let me start by saying I will NEVER have another RO system without a permeate pump again. Permeate pumps use the wastewater that is expelled during the RO process to greatly increase water pressure at the RO faucet, minimize wastewater and fill the tank in less time. They can be installed on nearly all standard RO systems aftermarket so there’s no need to buy a bundled RO system that includes the permeate pump (since most of those cost a lot more than buying the units separately). I was introduced to permeate pumps about 4 years ago. I purchased a Watts Premier RO system from Costco (when they still sold Watts Premier) and had it installed by a plumber (since I needed a hole drilled in my granite countertop). I consider myself pretty handy and although plumbing in general isn’t rocket science, I’m a large framed man that hates trying to squeeze under sinks to do pretty much anything plumbing related. After the RO was installed, I was getting smaller (and broken) pieces of ice at my refrigerator since my RO was feeding my ice maker through a longer 1/4” line from the kitchen island to the refrigerator. This a drawback of a lot of RO systems which feed ice makers that aren't in very close proximity. After researching I came across a permeate pump (sold through Watts Premiere) and made the purchase. The included instructions were specific for the RO unit I had and it was an easy install since the RO was already up and running. Immediately, you will notice several things with the permeate pump. 1) Permeate pumps make some noise. They generally click or “thump” every few seconds. This happens because the wastewater from the RO builds up pressure inside the pump that is then used to push fresh (permeate) water into the storage tank. When the pressure builds and releases, you get clicking or thumping until your tank is full. 2) Your RO faucet pressure increases dramatically. As a result of the increased permeate water being forced into the storage tank, the tank pressure within the tank bladder increases and you end up with water pressure comparable to your regular faucet. The line pressure at the refrigerator & ice maker (assuming you have them all hooked together) is also the beneficiary of the increased pressure and you get full sized ice cubes again. So, why wouldn’t everybody want one of these? Well, I think most people have never heard of them. If you have, then the results speak for themselves. HOWEVER, these do make noise...especially if your RO faucet has an air gap (that little hole in the back of the faucet that inevitably leaks water out of it when the drain line gets blocked with something). With an air gap, permeate pumps get VERY NOISY. The pump action not only clicks (or thumps) under the sink, but the air gap sound created from the pump gets much louder as well. The air gap noise on my Watts Premier Pure Plus unit was so loud I actually debated on getting another permeate pump in our new house. I ended up buying a highly reviewed non-air gap RO system from Amazon and had it installed for a month in my new house. As usual, the water taste and purity was perfect and I am pleased that my ice cubes were normal sized (since the builder installed a larger RO line from my island to the fridge). I just realized how much I was missing the RO tank pressure (which equates to faster filling of water jugs & cooking pots). I went back to Amazon and found this permeate pump which said it was the newer model that makes less noise. The unit arrived in about a week (no 2-day prime shipping available for it). I watched a YouTube video for installing it on a basic 5-stage RO and had it all hooked up in about 20 mins. I’m once again in RO bliss. The water pressure in the faucet just makes me smile...no more waiting a minute to fill a normal glass with water (OK it’s not literally a minute but felt that way to me). The noise is considerably less from the pump itself. I ended up buying some u-shaped plastic clamps (Amazon search: TmallTech Big Simple Clip Clamp 2.5" Bracket Reverse Osmosis RO Membrane Housing (Pack of 3)) that hold the permeate pump to one of the RO filters so the pump is not directly mounted to the cabinet wall (like it was at my previous house). Also, since I don’t have an air gap on this RO faucet, I have no additional noise from the faucet. If my house is silent, you still hear the pump cycling the water, but it’s minimal and it’s only until the tank is full. After that, it doesn’t cycle back on until water has been used from the tank. All in all, I missed the permeate pump benefits and will never have another RO system without one. I will also make sure I don’t get an RO with an air-gap faucet either. Hopefully this review helps people.