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I have a canopy which has drainage that runs into a water butt. It uses piping to which is about 8 foot off the ground and sloped towards the water butt and then has piping dropping vertically down into the butt. The water butt doesn't have any dedicated overflow pipe as I felt that if the water butt overflowed then it will just spill out from the top and run off into the grassy bit of the garden (which is fine).

So, the other day when there was a lot of rain, I noticed a lot of leaking of water from the canopy drainage pipe that leads into the water butt. My dad thought it was because the full water butt was causing a backlog of water but I didn't think this was possible. I thought that water levels would try to balance and because the water butt is at a lower level, it would just overflow. How can a full water butt cause a backlog into pipes which are at a much higher level.

Can anyone help explain as this does not make sense?

rapidnailer07 wrote: How can a full water butt cause a backlog into pipes which are at a much higher level.

Can anyone help explain as this does not make sense?

Physics was never my strongest subject, but I think it could happen if the outlet from the pipe was near the bottom of the water butt - the pressure of water in the butt exerted at the pipe exit point could be greater than the pressure of water coming in.

A more likely explanation is a restriction/blockage in the pipe leading to the water butt resulting in a build up of water above the blockage and the leakage you noticed.

ayjay wrote:

rapidnailer07 wrote: How can a full water butt cause a backlog into pipes which are at a much higher level.

Can anyone help explain as this does not make sense?

Physics was never my strongest subject, but I think it could happen if the outlet from the pipe was near the bottom of the water butt - the pressure of water in the butt exerted at the pipe exit point could be greater than the pressure of water coming in.

A more likely explanation is a restriction/blockage in the pipe leading to the water butt resulting in a build up of water above the blockage and the leakage you noticed.

You might be on to something, I do believe the pipe that feeds water into the water butt is quite long and goes down near the bottom of the container (if not the bottom, at least more than half way). Could this be the issue? Should the pipe be just long enough to reach the top of the water butt to solve the problem?

Too long a pipe is definitely the problem.

I'd keep it above the top-most water level.