I saw a video showing a water bowl for a cat that used an upside down PET bottle to provide "fresh" water when cats consume some of the water in the bowl. I wanted to design something similar.

Here is a very very high level sketch:

enter image description here

The idea is that an upside down water bottle is screwed into the top hole (on the left) and some sort of piping will lead the larger hole on the right to fill up with water. Naturally due to the pressure the water will overflow in the hole on the right.

My question is: Is there a way to prevent the water from overflowing in the lower basin when a water bottle has much more water stored than the basin can hold? I am very unversed in those topics so I unfortuantely even failed to find the right terms to search for in google...

  • $\begingroup$ If the piping between the two is too narrow, it will not work well, therefore be generous. $\endgroup$
    – Jim Clark
    Commented Aug 20, 2021 at 14:10
  • $\begingroup$ When the main "watering" bowl water level falls below the top opening of the traversal pipe, air will burp into the reservoir and release water. Set the top of the traversal pipe at the top allowable level of the "watering" bowl. You also want it to be easy to clean out occassionally. $\endgroup$
    – Jim Clark
    Commented Aug 20, 2021 at 19:21
  • $\begingroup$ get a bottle and experiment ... it is not very difficult to figure out what prevents the bottle from emptying $\endgroup$
    – jsotola
    Commented Aug 21, 2021 at 1:41

3 Answers 3


The water level in the lower basin will not exceed the level of the bottom of the bottle opening. When the empty device is loaded with a full bottle (by keeping the bottle upright!) and then inverted, the basin will allow air into the bottle, which in turn allows water to enter the basin.

When the basin water level reaches the opening of the overturned bottle, air can no longer enter, which prevents more water from leaving.

As water evaporates or is consumed by the pet, the lowered basin water level again allows air to enter, repeating the cycle.

There is a bit of disparity between the bottom of the inverted bottle and the top level of the water, which is related to air pressure. For additional information and possibly some involved mathematics, consider to search for "physics of inverted bottle water dispensers." There is a Physics SE related question which nearly matches your question.

  • $\begingroup$ Argh, blimey, that was exactly my first train of thought but then I had started to overthink it and came to the conclusion it will level out when the level of the bottle equals the level in the basin. But yea, it obviously cannot drain anymore when no air can enter it $\endgroup$ Commented Aug 19, 2021 at 23:04
  • 3
    $\begingroup$ It's important to note, however, that this only works when it's in its intended orientation. If your pet knocks it onto its side, then the majority of the bottle will drain onto the floor, creating a larger mess than knocking over a regular water bowl, and being easier to knock over the the first place due to the higher COM. I would include stability as a primary design goal. $\endgroup$ Commented Aug 20, 2021 at 8:41
  • $\begingroup$ Two nice Physics answers. Just don't make it 10m tall! $\endgroup$ Commented Aug 20, 2021 at 17:58

Works on the Toricelli vacuum - check out the barometer


Here is an idea from Chewy.com. Pay attention to the lid design, I think the basic idea is to rely on the buoyancy in the feeder tray to push/raise the lower component to block the release holes on the lid connected to the feeder bottle.

enter image description here

  • $\begingroup$ I agree, thats what I want, but how exactly does it work? How does it prevent all of the water to run out of the bottle? $\endgroup$ Commented Aug 19, 2021 at 22:44
  • $\begingroup$ The reason why I would like to know how exactly it works is that I want to design my own and have it printed on my 3d printer, therefore I need to understand the mechanics behind it :) $\endgroup$ Commented Aug 19, 2021 at 22:48
  • 1
    $\begingroup$ maybe a float that shuts off the flow when it rises a few cm? $\endgroup$
    – Pete W
    Commented Aug 19, 2021 at 22:54
  • $\begingroup$ My guess is the lid consists of two parts - fixed upper with holes, and floatable lower part - when water is at the low level, the bottom part will drop to release water, and float after the water has reached the designed maximum level. Just some calculation once you have determined the size and material of the lid. $\endgroup$
    – r13
    Commented Aug 19, 2021 at 22:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.