Unfortunately most home buyers don't even know what a pre purchase plumbing inspection is and when asked if they have had their plumbing inspected they say yes we got the building inspection done before we bought the house.
The problem is that 99% of building inspections do not cover plumbing! Plumbing to a house is one of the most essential parts of a household, it supplies you with clean fresh water to drink, water to bathe and shower in, water to your washing machine to clean clothes and waste disposal. Imagine living without any one of these essential elements, it would make simple things we do every day very difficult and time consuming.
The costs of fixing plumbing problems can go into the tens of thousands of dollars. The most common problem in house plumbing is tree roots penetrating the pipes. Tree roots grow where there is an abundance of oxygen, water, and nutrients which will eventually take them to water pipes. Tree roots in the pipes will cause objects and waste to get caught and eventually will build up and cause a blocked drain or can even cause the pipes to collapse. Another problem is the soil compressing and shifting when it gets wet and then dries out this puts a lot of pressure on the pipes which can cause them to collapse or crack. This will cause blockages and in unlucky cases the water can flow out the leak and into the soil which will cause the soil to erode (undermine) creating space between the pipe and the surface.
An undermine can happen from any broken or leaking pipe and can cause significant damage when the space between the pipe and surface collapses this can happen anywhere from under your house to under your driveway. If an undermine happens below your house it can damage the foundations which can cost $10,000s of dollars.
This is why a plumbing inspection is just as important as your building and pest inspection. When you're going to spend your hard earned money on a house make sure you get a plumbing inspection.