Drip irrigation is widely used in a range of different farming systems. Farmers generally adapt drip irrigation systems to their specific conditions. Irrigation performance is usually related to the hydraulic parameters of drip irrigation, and is usually expressed as a single static value. We developed a comprehensive approach to account for irrigation performance as a dynamic process, which evolves continuously due to changes in the way farmers schedule irrigation and renew irrigation equipment. The performance of drip irrigation systems used for greenhouse horticulture was evaluated in south-east Algeria in the 2012–2013 growing season. Two indicators were evaluated—distribution uniformity and water stress level. The approach was applied to 25 greenhouses owned by 13 farmers. Results revealed that the performance of drip irrigation systems is a dynamic process. We showed that farmers have integrated certain irrigation performance indicators such as distribution uniformity and water stress levels in their practices, as they have visible effects on crop production. Conversely, the relative irrigation supply does not directly interest the farmers, and was consequently not incorporated in their irrigation practices. We conclude that measuring drip irrigation performance must be accompanied by a broader understanding of the farming systems in which drip irrigation is used.