My parents just built a new house, but they've been having an issue where neither of the two toilet bowls is filling with enough water. I took a look at them (I know nothing about plumbing but I know how to Google) and discovered that the refill tubes weren't attached to the overflow tubes and most of the water was just filling the tanks rather than the bowls. I clipped them on and it did help, but the water level is still lower than ideal in both bowls. There seems to be a good flow coming from the refill tubes and since it's a new house I don't think there could be any blockages, there's plenty of water in the tanks (they're filled to the water level line on the overflow tubes), and plenty of water in the flush. The fill valves don't appear to be leaking and the tanks are filling at a decent rate. The only thing I can think of is that the overflow tubes aren't the right height for these tanks, but is that likely/possible? It just seems like if the overflow tubes were higher, there would be more time to refill the bowls before the tanks reached the correct water level. Currently, the tanks are about half full and are perfectly level with the water level lines. Does anyone have any suggestions?

Toilet tank image

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    Some toilets are designed to have less water in the bowl than others. Take a big jug of water and slowly pour the water into the bowl (dumping it in fast will effectively flush the toilet). See if the water level comes up in the bowl or ends up at about the same level you're seeing after a flush. That will let us know what we're dealing with. – poorplanning Jan 26 '18 at 23:47
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    Ok, after adding about 3 quarts of water at a slow trickle, the water level in the bowl hasn't increased at all. So that means it's just the design of the toilet? There's no way to adjust the amount of water that will sit in the bowl? – Lindsey735 Jan 26 '18 at 23:59
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    Correct. If the water level is unacceptable, you would have to replace the toilet. – poorplanning Jan 27 '18 at 0:01
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    Modern Low-flow toilet... – Harper - Reinstate Monica Jan 27 '18 at 0:25

The level of water in the bowl is fixed and depends only on the geometry of the S-bend that is part of the toilet

Toilet cross section

If you add one drop of water into the bowl, it will raise the level at the left side and one drop will fall down the waste pipe.

The only exceptions would be

  • installing the toilet on a slope would change the amount (but still fixed)
  • if the waste pipe is not at atmospheric pressure due to inadequate venting
    • water can be sucked out
    • excess pressure would push water back into the bowl (and there would be a flow of bubbles into the bowl)

None of which helps you. To get more water in the bowl you need a different design of toilet.

The syphonic action might mean that if the flow from the tank cuts off sharply, there might be room for more water. However the toilet is designed so that the flow from the tank continues, refilling the bowl completely, after the syphon has initially drawn out all the bowl's contents.


Based on clarifications provided, the toilet is behaving as expected. Nothing is wrong with it, and there is no real adjusting it.

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