Results from analysis of water samples from both outfalls (extract)
| Determinand | Outfall 1 | Outfall 2 |
| Boron (mg/l) | 0.16 | 0.20 |
| Cadmium (mg/l) | <0.004 | <0.004 |
| Copper (mg/l) | <0.002 | <0.002 |
| Iron (mg/l) | 0.26 | 0.18 |
| Lead (mg/l) | <0.01 | <0.01 |
| Mercury (mg/l) | <0.001 | <0.001 |
| Zinc (mg/l) | 0.06 | <0.02 |
| Biochemical Oxygen Demand (mg/l) | 3.50 | <1.90 |
| Chloride (mg/l) | 230 | 545 |
| pH | 7.8 | 7.4 |
| Total Suspended Solids (mg/l) | 3 | 42 |
taken from: Technical Reason for the Task. Welsh Harp Reservoir Reed Bed Feasibility Study, Halcrow, May 2001