Flush and fill activities are a critical but often underestimated part of bringing new data center cooling systems online, with significant implications for water demand, wastewater handling, and project schedules. This presentation shares practical insights into how flush and fill programs are planned and executed, including water sourcing, chemical selection, wastewater characterization, and coordination with local utilities. Using a real project example, it highlights why early planning and system-level thinking are essential to avoid delays, unexpected costs, and permitting challenges.