River of the World — Chaz Brenchley

The two cities of Maras-Sund are bound by an otherwordly bridge the Marasi used to conquer the Sundain. With their own magic over the water diminished, the Sundain's only hope for liberation lies with a man of limitless but untested power...

Possessing an affinity for water unparalleled by any of his people, Issel has led a small band of resistance fighters across the river from Sund to Maras in an attempt to break the magic binding the lands. They've taken refuge in the cistern network beneath the city, but in the presence of so much water, Issel finds his abilities overwhelmed -- and threatening to tear him apart.

The rebels find an ally in Jendre, the daughter of a general in Maras' army, who has her own vendetta against the regime. Her sister is held captive, along with others whose life essences power the magical bridge between her land and Sund.

Under other circumstances they would have been enemies. But in these extreme times, Issel and Jendre are the last hope of their two suffering peoples...