What Is Water and Wastewater Engineering?

Water and wastewater engineering is the branch of civil and environmental engineering that plans and designs the systems that make water safe to drink, deliver it under pressure, then collect used water, treat it and return it to a stream, the ground or a reuse customer. If a project needs a well, a treatment plant, a tank, a pump, a pipe or a sewer, this is the field that designs it.

What does water and wastewater engineering cover?

Two connected systems: the water system that brings water to people, and the wastewater system that carries it away. The engineer sizes, designs and permits both so they work on day one and at buildout.

• Water supply: the source (river, lake, reservoir or well), treatment, storage tanks, and the pipes and pumps that hold pressure.
• Wastewater collection: gravity sewers, lift stations and force mains that carry used water to treatment.
• Treatment: plants that make source water drinkable and make wastewater clean enough to discharge or reuse.
• Permits: the approvals each piece needs before it is built, and the limits it meets once it runs.

What do water and wastewater engineers do?

They turn a demand number into drawings a contractor can build and an agency can approve. Most of the work happens before construction starts.

• Estimate demand and flow, including peak water use and wet-weather sewer flow.
• Model pipe networks and sewers for pressure, velocity and capacity.
• Select treatment processes and size the tanks, pumps and filters.
• Prepare plans, specifications and the engineering report the regulator reviews.
• Support bidding and construction so what gets built matches what was approved.

For wastewater work in Texas, the engineer is defined by rule. TCEQ's wastewater design definitions at 30 TAC §217.2 describe a professional engineer licensed by the Texas board with expertise in treatment facilities and collection systems, and the submittal rule at 30 TAC §217.6 requires that engineer's signature and seal on the summary transmittal letter the owner submits for the project.

How does a water system get water from the source to the tap?

Water engineering, the supply side of the field, works in four steps: source, treatment, storage and distribution. Each step is its own design problem.

The CDC's overview of how water treatment works notes that lake, river and reservoir water typically needs more treatment than water from underground. It lists the common steps as coagulation, flocculation, sedimentation, filtration and disinfection. Which ones a plant needs depends on the source and what is in it.

Under the Safe Drinking Water Act, EPA has set standards for more than 90 contaminants, published as the National Primary Drinking Water Regulations in 40 CFR Part 141. Pressure is a design criterion too. In Texas, 30 TAC §290.44(d) requires a distribution system designed for at least 35 psi at all points at 1.5 gallons per minute per connection, and at least 20 psi under combined fire and drinking water flow where it is meant to fight fires.

What is wastewater engineering?

Wastewater engineering is the other half: collecting used water and treating it before it leaves the system, from the building sewer to the outfall or the reuse meter.

Collection runs by gravity wherever the ground allows. Where it does not, a lift station pumps the flow up and a force main carries it under pressure. TCEQ's definitions describe a lift station as a structure that collects wastewater and uses pumps to raise it to a higher elevation, and the collection system rules starting at 30 TAC §217.51 cover gravity sewers, lift stations and force mains. Choosing between gravity and pressure sewer systems is one of the first calls on a new system.

What is wastewater treatment engineering?

Wastewater treatment engineering is treatment plant design: the plant that removes solids, organic load, nutrients and pathogens so the water can be discharged or reused. Each unit process gets sized for the flow and the load.

30 TAC Chapter 217, Design Criteria for Domestic Wastewater Systems, is laid out much the way a plant is: collection, preliminary treatment, activated sludge, fixed film and filtration, natural treatment, sludge treatment, and chemical or ultraviolet disinfection.

The federal floor for a municipal plant is secondary treatment. Under EPA's secondary treatment standard at 40 CFR §133.102, the 30-day averages for five-day BOD and suspended solids may not exceed 30 mg/L, the 7-day averages may not exceed 45 mg/L, and the plant must remove at least 85 percent of each. EPA's secondary treatment standards page calls these minimum requirements. The plant's own discharge permit sets its actual limits.

Small plants follow the same chain at a smaller scale, as in this replacement wastewater plant project for an RV park.

What permits does a water or wastewater project need?

Usually two kinds: approval of the design before it is built and, for a plant that discharges, a permit to discharge once it runs.

EPA's NPDES permit program, set up in 1972 under the Clean Water Act, regulates point sources that discharge pollutants to waters of the United States, and EPA authorizes states to run much of it. In Texas, that permit comes through TCEQ's TPDES program. Design review is separate: Chapter 217 covers domestic wastewater systems, and 30 TAC Chapter 290 covers public drinking water systems.

Who hires a water and wastewater engineer?

Anyone who owns, builds or approves water and sewer infrastructure.

• Utilities, municipalities and special districts planning upgrades or expansions.
• Developers who need water and sewer service where no existing provider can serve.
• Civil engineering firms that need a specialist for a plant, a lift station or a permit.
• Contractors and design-builders who need a designer of record.

A utility's work usually starts with what is already in the ground: condition, capacity and compliance history. That first step differs from a greenfield site, which is why engineering for utilities and municipalities is its own practice.

What should you have ready before you call an engineer?

Five answers turn the first call into a feasibility conversation.

1. Do you know the site boundary and which water and sewer providers are near it?
2. Do you have a count of lots, units or connections, and a rough phasing plan?
3. Have you asked those providers whether they can serve the project?
4. Do you know where treated wastewater could go: a sewer, a stream discharge or reuse?
5. Do you know the date that drives the schedule?

If you can answer yes to the first three, an engineer can start a feasibility review; if not, those answers are the first task.

A note on scope: this is general education. The federal and Texas rules are summarized as published when this was written, other states have their own criteria, and the reviewing engineer and the agency decide what applies to a specific project.

Frequently asked questions

Is water and wastewater engineering civil or environmental engineering?

Both. The NCEES PE Civil exam is offered in a Water Resources and Environmental discipline, and NCEES also offers a separate PE Environmental exam.

What is the difference between water and wastewater treatment?

Water treatment makes source water safe to drink, under the Safe Drinking Water Act. Wastewater treatment cleans used water before it is discharged or reused, and the discharge is regulated under the Clean Water Act. Some processes appear in both, such as settling, filtration and disinfection. The targets and permits differ.

Is water services engineering the same thing?

Often. The phrase is used for the public water and sewer service a utility provides, which is this field. In building design it can mean the plumbing inside a building, which is a different discipline.

I manage a small wastewater plant for a Texas city and our flows have climbed all year. When do the rules say we have to start planning an expansion?

Watch the 75 percent line. Under 30 TAC §305.126(a), flow at 75 percent of the permitted average daily or annual average flow for three consecutive months triggers engineering and financial planning for expansion. At 90 percent for three consecutive months, the permittee must obtain authorization to begin construction. If the population to be served or the waste load is not expected to exceed the plant's design limits, the permittee submits an engineering report supporting that instead. Start the study well before the 90 percent trigger.

I'm developing a 200-lot subdivision in Texas outside any city's sewer service area. Which engineer do I need first, and what will they look at?

Start with a wastewater engineer, because the sewer answer usually shapes the site plan. They will check whether an existing provider can serve the site, compare a connection with an on-site plant, and look at where treated water could go. A plant is designed under Chapter 217, and a stream discharge needs a TPDES permit. The water side gets the same review against the Chapter 290 rules.

Related resources

• The Civil Engineer's Role in the Wastewater Treatment Process
• Understanding Your Community's Wastewater Collection System
• Understanding Lift Stations: A Walkthrough of Force Main and Pump Sizing Calculations
• Fire Flow Analysis: Engineering Solutions for Municipal Water Distribution Systems

Planning a water or wastewater project and not sure where to start?

MES designs water and wastewater systems for utilities, municipalities, developers and engineering firms, from the first flow estimate through construction administration.

Modern Engineering Solutions, McKinney, Texas, with offices in Golden, Colorado and San Jose, California. (214) 833-6748.

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