The new EU regulation for agricultural reuse defines minimum quality requirements for reclaimed water as well as performance targets for indicator organisms E.coli (≥ 5 log reduction), coliphages (≥ 6 log reduction), and C.perfringens spores (≥ 4 log reduction) that need to be met in 90% of samples during a validation monitoring. This presentation will focus on the design of UV reactors for final disinfection of reclaimed water, highlight challenges from different projects, and outline research needs to improve accuracy of reactor design. Since UV disinfection is typically the final barrier, definition of target log reduction values (LRV) needs to account for performance of upstream processes. Resulting UV doses to meet LRV targets can be derived from dose-response measurements in standardized collimated beam device testing. However, while plenty of data are available for E.coli and coliphages, only few studies reported dose-response data for C.perfringens spores. In addition, abundances of indicator organisms are often too low for verification of performance targets with standard analytical methods. Although the EU regulation considers treatment as compliant when indicators are absent in reclaimed water, little is known on the inactivation efficiency of coliphages and C.perfringens spores at low inlet concentrations, especially in a wastewater matrix.