Plumbing in the Home/Question
If one is purchasing an old home, how does one check underground to determine the condition of the lines (water pipes etc.) to determine if they need changing?
I know that changing pipes and lines can cost alot, are there any economical alternatives.
How long are typical pipes / lines underground supposed to last and are there any alternatives that can last for over 100 years for setting lines, pipes etc. - to avoid major excavation cost in the future when it comes to repairs required.
Things may be different in Trinidad. I am really only aware of common practices here in the US.
Up until the 70s or 80s, the main house sewer lines were typically the vitrified clay pipe with Bell and Spigot mortar joints. This is a great material for the use but the downside is that it can be fragile in the joints are very on flexible and subject to damage and penetration. If undamaged from outside forces, this piping system could easily last 100 years. Unfortunately, it is subject to damage from ground settlement, earthquakes and tree roots among other things. The only time it actually needs to be replaced is when it is damaged to the point that it is unserviceable.
Starting in the mid to late 80s, they switched to plastic pipe. Either ABS or PVC. This material is very durable with a lifespan in excess of 500 years or more. The joints are called "solvent welded" joints that use a chemical glue that actually melts the joints together forming one continuous piece of pipe.
The only feasible way, short of digging it up, is to use a piece of special equipment called a sewer camera that is run down the line. This equipment allows the operator to actually view with the camera is seen on a small screen while they are pushing the camera down the line as well as recording a video of the entire process. If the camera shows a breach in the line, there is an associated piece of equipment that can help them locate exactly where and how deep this breach has occurred. Around here, the service costs about $200-$300. While that seems like a lot, in comparison to many thousands of dollars to replace the line it could be considered a bargain.
Domestic water piping underground has been galvanized steel piping for many many years. In the last 30 to 40 years, copper piping or PVC plastic is pretty much the standard. Galvanized steel piping as a typical lifespan of 40 to 80 years. Copper and PVC, and less mechanically damaged can last over 100 years. There really is no way to determine the condition of underground water piping effectively.
The primary marker for failing galvanized steel underground water piping is a significant reduction in flow, typically caused by internal rust and mineral buildup.
Copper and PVC are not subject to these problems but they can be damaged and will usually show up as a leak in the piping. The way I determined that here is by shutting off the mains supply valve at the house if there is one and then monitoring the water meter for any changes. The meter shouldn't move if the pipe is not damaged and leaking. If it does move, then I know I have a problem somewhere that I need to find.
In your case, I would see if the sewer camera services are available for the main sewer line and have that checked. For the water service, if there are no records of it being changed in the recent past, I might be proactive and just change it out anyway to be safe if it is currently galvanized steel piping.
As for any "economical" alternatives for a complete sewer line change out, there really aren't any. There are alternatives such as relining the pipe with plastic but they typically cost about the same as a standard replacement under normal conditions. The only time "re-lineing" becomes cost effective is if you have a lot of extensive planting that would be damaged, a significant amount of concrete work such as walkways and driveways that would have to be repaired or some other non-standard condition like a significant hillside to deal with.