Should a drain pipe always have water in it?

It is one of the more common questions we do get asked, should my drains have water in them?  And there are two answers:

The first answer is YES:  Your sewer drains should hold water in certain locations.  The reason for the water in the drainage fixture is to prevent rodents and smells entering the building.  For example a toilet pan has water in its bowl always this is to prevent foul smells entering the building.  Other examples could be the J trap or shower drain these are also designed to hold water during normal operation.  If you do however notice excessively high levels of water there could be a blocked drain causing the problem.

The second answer is NO:  If you notice that drains are overflowing or making a gurgling noise or even sucking the water seal dry it would most likely point towards a fault in the drainage system.  The main sewer drain is designed to self cleanse (when installed correctly) and this is achieved by having the correct grade or slope on the pipe and therefore when any debris put into the line it will move along the pipe and end up in its correct destination.

Through using our CCTV drain investigation equipment we can identify areas of a drain which may be holding water due to a blockage or even a collapsed section of pipe.  When a drain has been newly installed or recently cleaned out there will be very little debris standing still in the line it will all move away promptly and this is how we identify problems by using our special equipment.

Today the water seals are becoming smaller so that aesthetically speaking they look more compact and fit into smaller spots.  In the image below you will see an example of a relatively new toilet installed in Hawaii, the water seal is quite present on this particular style of system, but not all are like this one.  Plumbing today is designed to be very hygienic not like many years ago when fixtures did not have water seals and rodents where present inside our sewage systems.