These days I rely on prints to do just about anything and find it rare when one fails. In this case it’s not from the printer or the filament but the design, possibly print settings and application.
Attached in a cross section of a male to female G1/2 coupler. I’m using it on a chiller so it sees low pressure water. the threads are not tapered so I’m relying on compressing rubber washers in the pocket where I marked it yellow. That’s also where it failed. its a simple failure, you lock the male threads down on to the washer and the part splits because it was printed 180 degrees from the photo. too little pressure and it leaks, too much pressure and the print splits.
I was on my third print and didn’t play with it anymore, but I think different filaments, % infill changes and print orientation might have help.
You could try printing it with 100% infill (if you haven’t done that) also reducing the part cooling and aux fan speeds can allow the entire part to stay warmer and thus bond together stronger. Beware that having the part and chamber become hotter can cause the PLA to deform and print poorly. Also you could change the CAD model so it looks more like this:
This would give it thicker and stronger walls so it won’t break as easily on the Z axis.
Well, there’s a reason why they’re usually made of metal: they can withstand 400 bar and temperatures of up to 200°C. I mean, printing them in 3D? It sounds dangerous to me if pressure builds up in the tube and it explodes.
As I understand it, you only allow water under light pressure to pass through. However, even that causes problems, as 3D-printed material becomes brittle when exposed to water over a period of months.
Maybe it’s better that it didn’t work out before you had the water leak. In my opinion, such a part cost a few dollars. I would advise against using water with 3D-printed parts in the long term, as they rarely coexist well.
Yeah PLA isn’t exactly suitable for long term usage especially at colder temps, but it could just be a part that @dean448 is printing to have something to use while the actual part is arriving. Though there is a chance it could work for a pretty long time if you design (and print) it well.
The danger part I don’t really get but I am the person who prints impellers out of PLA and spins them at 20,000 RPM 
The danger is rather that if it breaks, the apartment, garage, or whatever will be flooded with water and no insurance will pay for it. 
There is also the problem of achieving a proper seal: the water temperature can fluctuate. Even with cold water, the temperature can vary from 1°C to 30°C depending on the season, and it can be even higher if the OP wants to run warm water through it. This causes the PLA (or similar material) to expand and shrink, so it is difficult to achieve a tight seal. I’ve already started experimenting with this myself. For the garden? Yes, it works, and it doesn’t matter if water floods everywhere.
It should not be used for drinking water anyway, as plastic dissolves. However, I am not trying to lecture anyone here, this is just a friendly piece of advice. 
All good 
Makes more sense about insurance now too But drinking water?? For some reason I thought this was for something else, yeah PLA ain’t any good to drink and I would most certainly get a proper PVC or appropriate metal fitting to avoid even more microplastics in our bodies.
Some background. Using PTEG at 60% infill using some standard infill pattern. Coolant is RV antifreeze held between about 15 to 20 degrees C. A chiller for a laser.
Could have continued to play with it but I wouldn’t want it to fail some time in the future and leak coolant all over the machine. Thanks.