Drinking Water Distribution and Treatment

Getting safe water to the tap: demand projection, storage, distribution, and the treatment train — sedimentation, coagulation and flocculation, filtration and membranes, disinfection and its byproducts, hardness and softening, and processes such as air stripping. The NCEES spec gives it 6–9 of 80 questions across ten subtopics — breadth over depth.

What the problems look like

Mostly short calculations. Recurring shapes — fire flow from population or from building factors; demand at build-out with max-day and peak-hour factors; equalizing storage from a diurnal demand pattern and a pumping schedule; static pressure at a junction with a pressure zone or PRV in the network; ideal settling and overflow rate; alum dose and alkalinity consumed; flocculator power; filter count and backwash volume; CT and contact-tank volume with a baffling factor; hardness as CaCO₃ and split-treatment blending; and the Langelier index.

By exam day you should be able to —

• project demand and pick the right design flow for each component;
• size equalizing storage from a cumulative supply–demand curve;
• compute static pressure from HGL minus elevation, zone by zone;
• apply ideal-basin removal (vt/v₀) and know what depth does and doesn't change;
• compute coagulant dose, G-value power, and filter area with a unit out of service;
• compute CT, t₁₀, and required contact volume;
• split total, carbonate, and noncarbonate hardness in CaCO₃ units, and blend a bypass;
• judge whether an air stripper can reach a target from its stripping factor, size a carbon dose from an isotherm, and place the disinfectant to limit byproduct formation.

Where people lose points

• Design basis — build-out population, not opening population; served population, not county population; max-day for the supply that fills storage, peak-hour for what storage covers.
• Storage from the cumulative curve — the largest cumulative surplus minus the most negative cumulative balance, not the sum of deficit blocks or a rectangle at the peak rate.
• Pressure is HGL minus elevation. A PRV resets the HGL for its zone; the lowest ground carries the most head.
• Ideal settling depends on overflow rate, not detention time or depth; use the settling zone only.
• Right table row, right column — dynamic, not kinematic, viscosity for G; the stated temperature and pH for CT; the unbaffled factor when the stem says unbaffled.
• Hardness units — convert Ca, Mg, and HCO₃⁻ to CaCO₃ before comparing; carbonate hardness can't exceed alkalinity.
• Pressure at the tap — 2.31 ft per psi, gauge not absolute, met at the service connection's elevation, not the tank floor; the normal-working minimum is not the 20-psi fire-flow floor.

Have these at your fingertips

The fire-flow relation, ideal-settling relations, coagulant stoichiometry, the viscosity table, CT tables, and the equivalent-weight conversions — plus where they live in the Handbook. Design-standard questions draw on Ten States Standards — Water Works: the 2018 edition through the current window, the 2022 edition from the April 2027 exam. Know what it recommends versus its bare minimum.

Going deeper

• WRE design standards: the April 2027 change
• Hydraulics–Closed Conduit

Part of the Water Resources & Environmental exam. Practice this area with exam-real problems — the tutor walks any one you miss. → Start practicing free — free with an account.