While "doing business" in the Summerset Isles, which supposedly involved the death of Inquisitor Amolmaire, he read a book about the "Bloodspring of Lengeir's Feast," a fabled source of power for vampires. The book said the spring may be located in a buried ruin somewhere in Skyrim.
He arrived to Solitude and met Sybille Stentor who supported him and directed him to the Rift. After a few months he heard a rumor from a hermit named Jokull who had discovered red water pouring from the ground. Jokull had been digging a basement beneath his house, this basement was actually heading to the Redwater Spring. Jokull woke and burned the house while struggling with Venarus.
He then made some thralls to keep the digging. They were struggling for food sources but he realized that the Redwater Spring actually created disease to mortals with the addition of addiction. On the contrary, vampires gained powers but for a limited time only.
He then began to use the waters of the Bloodspring into the process for turning Moon Sugar to Skooma creating Redwater Skooma. He turned the basement into a den and began to lure people back, turning the disappointment of the spring into a ready supply of blood.