Quick take
A lab test is worth it when a health-related contaminant or private-well chemistry is driving a major purchase. DIY strips are enough for simpler operational questions such as hardness or free chlorine.
When lab testing pays for itself
Whole-house treatment, well-water systems and contaminant-specific purchases depend heavily on source chemistry. A broad or targeted lab panel can prevent buying the wrong technology.
When a DIY test is enough
Hardness, pH and free chlorine can often be screened cheaply and frequently. There is little reason to pay laboratory prices for every basic operating parameter.
Tap-level testing matters in older buildings
Lead, copper and plumbing-related contaminants can differ from utility-level data, making a household sample more relevant.