Looking at the reviews, there seems to be a consistent effort by what I take are some owners of the venerable Waterpik WP-100 Ultra to trash this new model and portrait it as inferior to the WP-100. I don't think this is the case, the WP-660 is an improvement over the WP-100 in many ways and I'll tell you why later. The funny thing is that when I bought my WP-100 about six years ago, there were some reviews from what I take were owners of the revered WP-60 Classic trashing the WP-100. I take some people prefer the old to the new and that's OK. But I think some reviewers are being unfair to the Aquarius I owned a WP-100 that lasted for little over six years, used almost every day by two people, those are a lot of days so the WP-100 is an outstanding product. I did have to replace the water reservoir once due to the cheap rubber valve mechanism -improved on the Aquarius as you will see- that failed after three years of use and started leaking. Also, the hook for the handle broke -also improved on the Aquarius- and it was very difficult if not impossible to hang the handle onto the Waterpik body, I had to makeshift a Velcro handle that looked terrible. Googleing around I was surprised to find that this is a common issue with the WP-100, some owners have replaced the entire unit just because of a broken handle as there is no spare part available from Waterpik. Boomer But other than those two issues, my Ultra worked flawlessly, I never had to replace the hose or the handle as some owners had to, the on-off switch never failed and it worked the same way it was when new until an accident damaged the power-cord and it stopped working. Given its state with the handle hook and its age, I thought about self-repairing it but then I decided it was time for a new unit. At first and reading all those pro-WP-100 anti-WP-660 reviews I was tempted to get another WP-100, but the price of the Aquarius was about the same as the Ultra so I decided to give it a try I'm glad I did. The first thing you notice with the Aquarius is its modern look and high quality materials, all white and clear, and gorgeous, a significant design improvement over the WP-100. It is also lighter, which some can argue is a good thing -like me- and some can argue it is a bad thing because it "feels" cheap, which is also a valid point. The important thing is that its weight doesn't compromise its operation in any way, it won't tip-off when used nor will slide or be unstable, it is just lighter. It might be due to the use of cheaper materials on the pump as some have argued here, or just lighter materials, an overall technological improvement rather than cheapening the unit off. I guess time will tell which one is more durable, or we will have to open both units and compare its guts to get a final answer. So, why is the Aquarius better than the WP-100, other than it looks? -The WP-660 is less noisy and runs smother than the WP-100, you notice this right away. This with no compromise to the water pressure, the pressure is steady, as or more powerful than the WP-100 but it runs better, it sounds less stressed. Same or better results with less noise. -The hook for the handle was replaced by a sturdier piece and a different design to hold the handle, which reduces the pressure on the piece. With the WP-100, it was very easy to push the handle all the way down the hook, either by accident or just because of its design, stressing the hook and eventually breaking it; there was nothing to stop the handle to slide all the way down. As said, mine broke. That was a poor design, fixed on the Aquarius; now you just put the handle on the holder, it cannot be pushed all the way down. Some have argued that makes it difficult to handle the hose, but I didn't find any issues, the hose juts hang there by simple gravity, it doesn't tangle or interfere with the unit in any way -The reservoir valve was replaced by a metal spring mechanism. This was a another design flaw of the WP-100, its reservoir valve consist of a rubber piece, very cheap in my opinion, which eventually gives up and start leaking after a few years. As said before, the only way to fix it is by buying an entire new reservoir as the little rubber piece is not available alone, which means not only paying way more but also a waste of resources. In contrast, the WP-660 has a stainless steel spring with a plastic cap, that appears way more durable and also a much better and higher quality solution. Only time will tell but it seems it will last longer than the one in the WP-100 -The knob to graduate the pressure is easier to operate. The WP-100 has a hole to put both fingers in, on the Aquarius is a protruding knob, very easy to reach and to manipulate, way better I think, easier to find when in use if needed. And also more ergonomic -The Aquarius handle has an on-off switch that actually works. The WP-100 has that dreadful push button on the handle that you need to press constantly to stop the flow of water, doesn't stop it completely and also causes the Waterpik to make a noise like the pump is being damaged while the pressure is reverted. Not good at all, it was a poor solution at best, a useless feature at worst, it just didn't work. On the WP-660, there is an actual on-off button; in fact the correct way to operate this new Waterpik is to turn it on the base first, then turn it on via the handle when you already have the tip inside your mouth ready to go, the water doesn't come out unless you turn the handle on. This is much better than having to reach the switch on the base unit with the tip in your mouth or having to hold into the appalling pressure cutting button on the handle and then release it. All this while water was still coming out of the tip as the button didn't cut the water flow completely. -The pace timer. This feature is non-existent on the Ultra, and I realized it is very helpful. I use the Waterpik first on the upper section of the mouth, outside-inside and then move to the lower section, in-out and I'm done. At a pressure level of 8, the water in the reservoir, at full capacity, should last little less than 90 seconds. The Aquarius will give you a very short flow pause at 30 seconds of use and another at 60 seconds, this is good to pace your cleaning as it should take about 30 seconds to clean each part of the mouth, up and down, and then you have an extra 20 seconds to touch-up. This avoids you having to be periodically peaking over to the reservoir to see how much water is left and instead allow you to concentrate on the cleaning and doing the job properly -The reservoir cover is now part of the unit. If you are like my mother in law that misplaces everything - sorry mom, I still love you-, chances are you have misplaced the reservoir cover of the WP-100 (as my mother in law did). This cover also contains the tips so it can be kind of an inconvenience to lose it. On the WP-660, the cover is attached with a hinge mechanism to the body of the Waterpik, no way to lose it. The tips are now stored on the unit itself, behind the reservoir The rest is about the same as the WP-100, it comes with a bunch of tips from which you will probably only use the classic jet, and a 3 years warranty. It also includes a gum massaging mode which is pointless as you can achieve the same results by regulating the pressure knob. One disadvantage to the WP-100 is that you can only store two tips on the unit and not four, but again if you are like me that use only one, this is not an issue. But it might be for some users, if you have braces for example or like to regularly use the one designed for root canal maintenance (the Pik Pocket). One thing that was bad on the WP-100 and remain as bad on the WP-660 is cable management, there is no place to wrap the cable or at least a Velcro band included to deal with the cable, this lack of cable management is in part responsible for the damage to my WP-100 power cord, the cord is just hanging there. A need
