An individual should have demonstrable personal wealth, in excess of 25,000 gp, that has been largely acquired through mercantile endeavors. (Adventurers who recover large amounts of treasure do not provide the same ongoing economic impact to Waterdeep as a wealthy merchant who employs hundreds of Waterdhavians.)
An individual should reside in Waterdeep except when wintering in the South or leading trade expeditions.
An individual should own several significant properties in the City of Waterdeep.
An individual should play a prominent role in one or more guilds.
An individual should be human. (Although some Lords might wish otherwise, the other families are unlikely to accept a nonhuman ennobled family any time soon.)
An individual should be "sponsored" by at least five other noble families.