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.
I was dissatisfied with the substandard service.
This country's technological capability is still at a low level.
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'.