Do you have gray plastic shut off valves and supply hoses under you sinks and toilets? If your house was built in the 1970s to the mid 1990s you could find this type of valve and hose under a kitchen or bathroom sink or possibly under the toilet.
The gray plastic fittings in these pictures are made of polybutylene. This was a standard plumbing fixture valve and hose material from the 70s to to the mid 90s. During this period, there were issues with polybutylene supply tubing in walls and crawlspaces developing leaks and the use of this material was discontinued around 1995.
I still run across these type of valves and supply hoses under sinks and toilets. Given the past long term issues and problems with polybutylene piping I always recommend replacing these valves and hoses with modern plumbing parts.
Brian Jovag, owner of Jovag Home Inspection.