Introduction

Despite the introduction of filtered water fill stations, it’s still annoying to get filtered water in a lot of hotels or at an airport. There’s existing solutions for outdoors use, but they often don’t have carbon filtration. There’s also existing solutions for travel use, but they’re usually only carbon, and don’t have ion-exchange resin for improved taste. You can buy pitcher filters that do this, but packing a water pitcher takes up a lot of space and you can’t as easily have it in a backpack. Hotels usually do have bottled water, but even if it’s free, it’s hard to get as much as you might want, and there’s a lot of waste.

Before we get started, note that this is only for filtering biologically safe water. If the water is unsafe, then I’d suggest a SteriPen to sanitize it. If the water is cloudy, this isn’t going to work so well, so you’ll need to add a flocculant such as P&G Purifier of Water first before further treating it.

Experimenting with ZeroWater

I’d originally started off with a ZeroWater because it deionizes water and you get to pick what minerals you want to add to it. And for places that might have questionable water treatment, it’s hard to beat it for removing heavy metals from the water. For this, I 3D printed a Zero Water Travel Filter. But there’s a few problems. One, it’s huge, and has gotten my bag sidelined for extra screening. Second, if you want the water to taste better, you’ll need to add your own minerals to it, so that’s more to carry. It works great for things like humidifiers to avoid mineral deposits, but I think for daily drinking water, it’s kind of overkill and annoying. Plus, the filters are expensive and there aren’t generic ones you can easily buy.

Trying other filters

I went to a Target and looked to see what they carried, since it’s easier to get more supplies at a big national store than it is to order them online. That doesn’t help me when I’m traveling abroad, but that’s not the majority of my trips. I’d wanted the ion-exchange resin in there because it tends to improve flavor. I landed on the Brita Filter Elite and the Pur Plus. I think on paper the Pur Plus filter does a better job, but in practice, the flow rate is so slow that it’s annoying. Tasting the water out of my faucet, the Brita Filter Elite tasted a little bit better too, so it won on flow rate and flavor. It’s true that it filters less, but I don’t need it to filter everything. Plus, there’s multiple brands of compatible filters. So I decided to build a design around that one.

Designing Around the Brita Filter Elite

I got this idea the day before going out of town and I didn’t have a lot of time to do a design. I’d started by taking the dimensions of the bottom of a brita filter funnel and making it just a tube with the filter on the bottom. That design was really compact and worked fine for wider bottles, but didn’t do the trick for the ~500mL Nalgene bottles that I like to bring with me. So I needed something a bit different. For the ZeroWater, I’d just balanced the filter on top of the water bottle and the drip out of the bottom of it didn’t really make a mess. For this one, I needed to redirect the water downward into the bottle.

I tried designing this one using gpt-5.6-sol in OpenSCAD with a source sketch, a bunch of dimensions with my calipers and some test models. I got a lot of the way very quickly, including the tapered design, bottle adapter, and rough filter snap, but I ended up having to do a lot of test prints to get the fit just right. I wanted to print it from the top on the build plate up, and the more complex parts were a little tricky.

But I did finally get it to work. The result is over here on MakerWorld: 16oz Nalgene Brita Filter Cup, and the corresponding caps for it Caps for 16oz Nalgene Brita Filter Cup. It holds around 175mL on the top, and travels pretty well. The tapered base means that you can stick it on the top of a lot of different wider bottles, and it can sit nicely on my Nalgene bottle.

A Note on Safety

I used transparent PETG for this design because PET is generally safe and used in a lot of things. Transparent PETG doesn’t have non-food-safe colors. There’s going to be microplastics, but it’s not much different than bottled water in many cases. That all said, now that I’ve found that this design works, I’d like to cast it in food-safe silicone. That will prevent bacteria from getting stuck in the inner parts of not perfectly watertight prints, and while silicone can suck up some smells, it’s easy to fix by baking in the oven, which also helps sanitize it.