循环式水培系统（也称为再循环或闭环系统）是一种将营养液从中央储液罐连续或定期泵送到植物，然后排回同一储液罐以供重复使用的系统。这与径流被丢弃的排水式系统形成对比。循环系统更具资源效率，但需要更主动地管理 pH、EC 和病原体控制，因为同一种溶液会反复通过根区。
关键事实
- Nutrient solution is recirculated rather than discarded — lower water and fertiliser consumption
- Examples: DWC, RDWC, NFT, ebb-and-flow, Dutch bucket with return lines
- pH and EC must be monitored daily — concentrations change as plants absorb differentially
- Pathogens spread rapidly through recirculating systems if root rot takes hold
- Full reservoir change every 7–14 days prevents salt and pathogen accumulation
- Requires a return drain from growing channels back to the reservoir