This article examines whether reclaimed-water irrigation leaves a detectable anthropogenic chemical signal in the lettuce (Lactuca sativa L.) rhizosphere when seasonal biology, root-zone matrix complexity, and ionization selectivity are evaluated separately. Eighteen rhizosphere samples were collected from tap-water, reclaimed-water 1, and reclaimed-water 2 treatments during fall 2021 and summer 2022, with three biological replicates for each treatment–season combination. The analytical sequence combined four specific evidence classes: acquisition-domain feature retention, designed-factor variance partitioning, polarity-specific annotation confidence, and compound-origin prioritization. Across positive MS1, positive MS2, negative MS1, and negative MS2 acquisition domains, 12,513 initial regions of interest yielded 10,046 retained features after blank and quality-control filtering, corresponding to 80.28% overall retention. Negative ionization retained 90.36% of its features, compared with 72.19% in positive ionization, indicating a root-zone chemical field enriched in negative-mode-compatible constituents. Designed-factor partitioning attributed 42.16% of total variance to season, 15.34% to irrigation-water type, 15.92% to the season–water interaction, and 26.58% to residual variation. Within the structured experimental fraction, season accounted for 57.42%, while irrigation-water type and the interaction contributed 20.89% and 21.68%, respectively. The annotation set comprised 37 tentative compounds: 31 endogenous or rhizosphere-associated constituents and six anthropogenic indicators, namely bisphenol A, fenoprofen, methylhexahydrophthalic anhydride, naproxen, terephthalic acid, and imiquimod. Reclaimed-water irrigation therefore produced a chemically visible indicator layer, but the broader rhizosphere profile was governed mainly by seasonal endogenous chemistry. These findings establish a season-resolved interpretation of reclaimed-water effects in which trace anthropogenic indicators are retained as monitoring targets without being allowed to dominate the biological reading of the rhizosphere profile.