Brita and Moving

My former, bless its soul, Brita filter and my recent move had something in common. Perhaps it would be more right to say that my former Brita filter and I had something in common. Never did I think I would write an essay comparing myself to a rather utilitarian object, yet here I am. Bewildered as you may be, questioning as you may of my sanity, I shall demonstrate I am indeed quite a bit like my former Brita filter.

If you think you know Brita filters and think you therefore know my former Brita filter, you are likely mistaken. You see, my former Brita filter, or more properly pitcher, or even more properly Stream Filter as You Pour Pitcher, which I’m just going to refer to as ‘Stream’ going forward so I don’t have to keep writing ‘former’ and all those other words, had this rather infernal design by which, as the most proper name suggests, the water is not actually filtered until you pour. The intent behind this is sound, but in practice it’s awful.

See the more traditional Brita pitcher design below:

The Brita Soho, image courtesy buybuyBaby

This one is called a Brita Soho, which is fitting because I now live in SoHo. Actually that’s irrelevant; moving on. Most Brita pitchers going back presumably to whenever Brita pitchers were invented have more or less been designed like this. One pours water into the opaque white section on top, and it, rather slowly per legacy filter design, flows through the filter hanging below. Filtered water fills the base of the pitcher and the capacity is demarcated by the line running along the bottom of the top section. The water is then ready to pour or be chilled in a refrigerator — just as with any other water pitcher, which is great, though there are some obvious downsides to this design, as anyone who has ever used one likely knows.

The problems originate with the fill chamber, that opaque white section up top. That fill section typically has a volume less than the base, which means one has to fill it, wait potentially quite some time, then fill it again to actually get a pitcher full of filtered water. Why not make that section bigger, you might say? One could maximize the fill chamber to be 50% of the total volume, meaning one single fill of the top chamber would provide a full pitcher full of water, but that leads into the next problem.

That fill chamber is wasted space. Once the water has passed, it’s empty, and that volume makes the pitcher much larger than a conventional pitcher for a given water capacity. As fridge or counter space can often be scarce, this is far less than desirable. One could make the fill chamber very small, but then you would have to fill it up more than 2 times to get a full pitcher. As there is no perfect solution, Brita engineers seem to have decided that the happy compromise is between 1.5–2 fills of the top chamber to fill the rest of the pitcher, meaningful the fill chamber is about 1/3 the volume of the the entire pitcher and the filter pitcher is about 50% larger than it would be without a filter. But wait! Perhaps there is a perfect solution. At least, that’s what the folks at Brita must have thought when they were designing the Stream.

It’s easy to infer the thought process behind the Stream. See below.

The Brita Stream, image courtesy Target

While gravity feeds traditional filters from the fill chamber leading to a top to bottom flow of water, in this case the flow is reversed as water flows from the chamber through the filter and out the pour nozzle. Naturally, you have to actually lift the pitcher and tilt it to pour for this to happen. Crucially, the problematic fill chamber is gone.

The innovation here is a filter that filters so quickly that it actually filters the water as you are pouring. That’s right — while you’re pouring. Surely, in the conceptual phase a fill chamber-less pitcher would have been a whet to all focus groups, consultants, and perhaps even Brita water filtration forum enthusiasts (there’s an online forum for everything, right?). Whoever came up with this must have felt like a hero. This design is far more space efficient and elegant looking that the traditional Brita filter. The entire pitcher volume can actually be filled with water. This sounds great but in practice, it sucks.

The first problem is that, even at its best, the filter is slow. Water doesn’t pour at the rate that it normally pours at from a pitcher. It pours at…must less than that rate. Worse, the filtration rate drops precipitously as a function of the amount of water in the pitcher. And this is the way that my Stream was like move.

Though I’d be lying if I said I fully understood the physics behind what’s happening in the Stream, it’s apparent that the change in flow rate is related to the water pressure upon the filter which effects the filtration rate through the filter which constrains the pour rate. Water pressure is directly related to height of water, meaning that if you double the height of water, the pressure doubles as well.

One quirk of this relationship is that the maximum height of the water or any liquid is determinant of pressure even when only a small portion of the total volume of water is at that maximum height, as in the case of oddly shaped water vessels, or the old western barrel explosion trick involving attacking a thin and very long, tall tube on top of a barrel and filling it until the barrel explodes due to the massive increase in water pressure. You can try the barrel trick by running a garden hose up to your roof, but be careful. Though this may seem puzzling at first, it makes sense if you imagine an array of vectors of gravitational force along the bottom surface of a vessel acting upon all of the water immediately above them, and then consider how those aggregate would be distributed. Similar properties make hydraulics work, which are all simply physics but essentially magic. Anyway, back to the point.

With a Stream, water pressure (height from pour nozzle to max water line) is actually maximized by tilting the entire pitcher more than 90 degrees (maximum water height would be achieved somewhere between 90 degrees and completely upside down, by my brain geometry estimation), which nobody would intuit to do, so practical maximum water pressure occurs at a 90 degree tilt. The moment you start pouring, the pitcher starts slowing as the water level naturally drops. This isn’t a big problem for the first few cups, but becomes a massive problem towards the end. By the time you’re down to a quarter pitcher the pressure is perhaps 1/4 of what is was when full, and thought I’m sure the filter is designed so the relationship between pressure and filtrate rate isn’t quite direct, even figuring 1/2 the filtration rate, which anecdotally feels about right, it takes twice as long to pour a single glass. And, it was slow even at the original rate. It’s pretty bad.

Now, I’ve seen play out before. Bath tubs do this — they drain fast at the top, then very slowly towards the end. But no one cares, because no one is in a rush to drain their tub in the way one would be in a rush to drink their damn water, especially when moving and sweaty and tired on the hottest day I ever experienced in San Francisco. Water moves more slowly towards the end of draining, as did my belongings toward the end of my move.

When I started removing items from my home, it moved quite quickly. Within an evening or two my apartment was half emptied. After the removers came, it was about 90% empty. After the movers came, it was about 99% empty. It took almost two full days to clear out that last percent of my belongings. Part of that was because the last few items were tedious to pack and organize, but a bigger part was that my psychology with the move mirrored my former Brita. When the pressure was high I moved fast. When it was low; when I was almost done, I moved comically slowly. I had much intention, but little follow through. There was so little to do but so little motivation to do it, because I was almost done; the pressure was low, so the throughput was low.

I wonder if all of my thinking through the physics of my Brita and pressure was for nothing. Perhaps it, like me, just gets lazy towards the end.

My former Brita Stream, now sadly departed, just prior to its final pours



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