This book examines the process of injecting treated wastewater into wells to replenish aquifers, and thereby slow the process of land subsidence, and help to mitigate coastal flooding. It explains how up to fifty percent of sea-level rise may be due to land subsidence, and up to fifty percent of land subsidence may be due to aquifer compaction. The concepts covered discuss replenishing aquifers with clean water to reduce nutrient discharges into out-falled waterways; providing a sustainable supply of groundwater; reducing the rate of land subsidence; and protecting the groundwater from saltwater intrusion. Practical case studies from Virginia and California will be included.