| Watford to Olivares | 1,022.97 mi (1,646.31 km) |
| Watford to Olivenza | 952.75 mi (1,533.31 km) |
| Watford to Olot | 668.37 mi (1,075.64 km) |
| Watford to Onate | 603.11 mi (970.60 km) |
| Watford to Onda | 807.90 mi (1,300.19 km) |
| Watford to Onteniente | 886.72 mi (1,427.04 km) |
| Watford to Orihuela | 937.94 mi (1,509.46 km) |
| Watford to Osuna | 1,022.56 mi (1,645.65 km) |
| Watford to Ourense | 732.86 mi (1,179.42 km) |
| Watford to Oviedo | 626.59 mi (1,008.40 km) |
| Watford to Paiporta | 844.82 mi (1,359.60 km) |
| Watford to Pajara | 1,759.27 mi (2,831.28 km) |
| Watford to Palafolls | 705.72 mi (1,135.75 km) |
| Watford to Palafrugell | 693.33 mi (1,115.81 km) |
| Watford to Palamos | 697.77 mi (1,122.95 km) |
