Civil Engineering is a broad field encompassing many sub-disciplines. Specifically related to water there are a variety of areas that civil engineers are involved.
Water Resources Engineering is a broad area of civil engineering that generally includes the rainwater or surface runoff, rivers and lakes and underground aquifers in large native or developed areas.
Storm Water Engineering generally refers to surface drainage in developed areas (and usually the grading involved to channel that water appropriately.)
Domestic Water generally refers to potable water that is treated at a facility and piped to residence and business taps.
Wastewater Engineering involves sewage that must be collected and transported to a local or municipal treatment facility or where permissible may be disposed of by an engineered septic system.
Definition