The origin of plumbing disputes arises usually out of defective work and/or materials. Building plans often lack critical detail regarding specification of water pipes, fittings and connections or it simply gets ignored and inferior fittings and pipes get installed. This is a cost cutting measure on behalf of the contractor and it is seldomly addressed in building contracts. Due to the nature of plumbing work defects will usually only be discovered much later on and then it will be hard to proof that the contractor or builder delivered inferior work or materials.
When one deviate from the plan as the building work progress its also easy to make minor changes when something seems better or more suitable as you go along. This usually result in piping and fittings being used that is not suitable. Even if there is no intention to use inferior fittings and piping this happens regularly.
It is of utmost importance to the contractor to take the time and implement the necessary quality assurance processes to try to eliminate any potential plumbing disputes, but unfortunately there is rarely enough time for this upon completion of a project, so this vital inspection often gets left out.