low-level; substandard
Describes something that is below an expected or acceptable standard, often used in economic, technical, or evaluative contexts.
The educational standard in this region is low.
This country's technological capability is still at a low level.
I was dissatisfied with the substandard service.
The unemployment rate has continued to hover at a low level.
This factory was shipping out substandard products.
低調 describes an activity or market being sluggish or in a slump, whereas 低水準 focuses on a numeric value or standard staying below a normal benchmark.
高水準 means 'high level/standard', the direct opposite of 低水準 which means 'low level/standard'.
low-level language
Compound of 低 (low) and 水準 (standard, level). The word 水準 itself is a Meiji-era coinage from Chinese-based morphemes, originally meaning 'water level' and later extended to 'standard'.