Radagast instructed you to pour the pure water into the sanctum of the Red-maid's fortress, Garth Agarwen.
'Thou must now enter the stronghold of the Red-maid at Garth Agarwen, as the Wizard instructed thee. Her sanctum is guarded beyond the walls of the mighty fortress. Men of Rhudaur still walk through the remains of their ancient home in service to the Red-maid and the Gaunt-lord Ivar.
'Thou must find thy way into her sanctum, call her by some means, and then defeat her. She will fall into the water, and the water will become still.
'When this happens add the pure water graced by a River-daughter's love to the pool. There are centuries of corruption and hatred layered upon the Red-maid, but we must begin somewhere. May the Valar go with thee, ${PLAYER}, for they have abandoned us.'
The Red-maid is in her sanctum within her fortress of Garth Agarwen.
Dannasen instructed you to obey Radagast and take the pure water to the Red-maid's sanctum. Once there, he told you that you would have to defeat the Red-maid, and when the waters of her pool go still, to pour the water in.
Dannasen is at the Eglan-camp in Agamaur.
You should return to Dannasen and tell him that you poured the pure water into the Red-maid's Sanctum.