I saw a house for sale today and my realtor and I couldn't figure out what this was attached to the water heater, some kind of water piping/tubing. We'll get to the bottom of it with the inspection, just impatient to know what on earth this is. House built in 1984.
It looks like PEX and has the white ring things that go over Uponor ProPEX style connectors. Here is a video of the material in use, pay attention to the expansion tool: https://www.youtube.com/watch?v=AXYONkaxzv8
You should confirm this observation by noting any markings printed on the tubing, they should say PEX somewhere. The house was built right in the middle of the polybutylene era, you want to be absolutely sure it is not that.
PEX would definitely not be original to the house as it did not exist in 1984. Why the piping was replaced would be a good question for the seller, it might actually be replacing polybueylene. https://www.nachi.org/pb.htm
That would be your water distribution system, aka supply plumbing. Cross linked polyethlene, or PEX for short; Using a manifold arrangement.
Most likely the red ones are hot water, the white ones are cold.
Only gets confusing if there's also a hydronic heating system also using PEX, but no more so than when they were all copper, or iron.