Implementing nutrient management strategies in soilless culture, which improve water use efficiency (WUE) and limit the loss of eutrophying elements without affecting crop performance, is a priority for the floriculture industry. The aim of the current research was to assess the effect of two nutrient management strategies, based on electrical conductivity (EC) or nitrate-nitrogen (N-NO₃⁻) concentration control on plant growth, ornamental quality, plant–water relations, mineral composition, and WUE of greenhouse Hippeastrum grown in semiclosed soilless system. The recirculating nutrient solution was discharged whenever a threshold EC value of 3.0 dS·m⁻¹ was reached (EC-based strategy), or when N-NO₃⁻ concentration decreased below the limit of 1.0 mol·m⁻³ (nitrate-based strategy). There were no significant differences in terms of plant growth parameters, stomatal resistance, leaf water relations, and macronutrient composition in plant tissues between the two nutrient management strategies. In the EC- and the nitrate-based strategies, the recirculating nutrient solution was flushed 10 and 5 times, respectively. The water loss (W_L) and the total water use (W_use) in the EC-based strategy were significantly higher by 261.1% and 61.5%, respectively, compared with the N-NO₃⁻-based strategy. In contrast with the EC-based strategy, the adoption of the N-NO₃⁻-based strategy significantly minimized the nitrate, phosphate, and potassium emissions to the environment. The effective WUE of the system (WUE_S) recorded in the N-NO₃⁻-based strategy was higher by 55.9% compared with the one recorded with the EC-based strategy.