Abtract: Supply and Distribution Systems

The university provides potable water (e.g. for drinking, research, instruction, cleaning, irrigation, animal husbandry, fire protection) and either owns and operates a water distribution system or works closely with a water supplier. Water quality must meet regulatory standards and be aesthetically pleasing. Main water supply elements are the water source, treatment facilities, storage system, and distribution system. A small rural school might manage all aspects of water supply, including identifying and caring for sources, but most universities are in a municipality or water district, so the distribution system is their focus.

Water Source

Main water sources are surface water (e.g., lakes, rivers) and groundwater (usually pumped from dozens to hundreds of feet  below  ground).  Groundwater  under the influence of surface water is a spring or shallow groundwater subject to surface  water  intrusion  or surface contaminant migration. Source protection programs inspect activities on and around the water source, prohibit activities that  could  cause contamination, and are tailored to water source type and intensity and to types of nearby operations.

Treatment Facilities

Treatment type depends on water system size  and source. Smaller systems need disinfection and possibly filtration; larger systems have treatment that uses disinfection and meets turbidity and contaminant-level requirements. Complex water treatment systems can have many unit operations (e.g., basic multimedia filtration, ultrafiltration, reverse osmosis). System operators must know basic information on  treatment and water sources (e.g., by touring and acquiring information from water treatment operators).

Storage Systems

Areas with flat topography can need elevated water tanks to provide water pressure, balance supply over daily or extreme use variations, supply water during a pump failure or power outage, and size system pumps to meet lower flow volumes. Operators must watch residence time in these tanks, which need regular maintenance (e.g., inside and outside painting, disinfection, vent screen checks). Booster pumps and storage tanks are common on buildings too tall to be served by street pressure. Buildings with fire sprinkler protection need backup power (typically an emergency generator).

Fire Protection. Campus fire protection is often part of the domestic water distribution system. Many factors (e.g., occupancy load, building size, construction materials, usage) affect fire flow requirements and protection measures for each building, set by the state fire marshal and local fires protection districts.

Distribution Systems

Design of Piping Networks. The earliest  U.S.  water systems used wooden water mains, but cast iron, steel, and copper were standard for much of the 20th century. Recent plastic pipe advances (e.g., high-density polyethylene and PVC)  have  weight  and  cost advantages, but issues arise with  the  pressure  ratings and still-unknown longevity of these systems (e.g., connection reliability, organic chemicals leaching into water). For  water distribution system designs, criticality  of water supply to each building type (e.g., critical research; HVAC equipment  using  makeup  water)  must be analyzed so that the water  system  design  (or upgrade) loops the water distribution piping network and feeds water to critical buildings from multiple sources, using an adequate number of valves (based on a rule of thumb and what-if analysis of water main breaks and repairs, based on water system  maps)  to  isolate  pipes for repair and maintenance and minimizing radial feed legs and dead legs  (e.g.,  fire  hydrants,  abandoned feeds). In looped systems, water  follows  the  path  of least resistance; if the distribution system has different pipe sizes, water flow will be low, leading to water  residing in the pipes too long, degraded water quality,  and even virtual dead legs, but regular directional flushing can help. Design should minimize pressure drops in the system.

Conservation Versus Quality. Water conservation is an important part of a sustainable future, especially in arid areas (e.g., the U.S. West). Drinking water contaminant levels are based on concentration, so more water moving through a distribution system makes it more likely that water quality meets relevant limits. Large quantities of moving water prevent water stagnating in pipes and picking up rust and contaminants. High water age (caused by low flow) reduces disinfectant concentrations (leading to bacteria growth) and exacerbates disinfection byproduct formation. Water distribution system designs provide more than adequate flow capacity for the largest demand (fire flow), resulting in oversized mains and service lines and stale water (e.g., warm, bad tasting, containing bacteria or disinfection byproducts). Computer-based models require time to set up but can test system changes before implementation.

Operations and Maintenance. (1) Distribution  system maps support O&M, minimal mistakes, modeling, replacement and rehabilitation planning, and water  quality problem identification. As system maps are developed and updated, facilities  managers  consider valve sites; main locations,  sizes,  and  materials;  pipe age; and  breaks  and  complaints.  Mapping  uses AutoCAD software, GIS software, or both and marks valves, fire hydrants, meters, and backflow preventers, relying on field measurements and observations and on continual and prompt updates. Methods to locate valves  in the field vary  based  on  user  resources.  (2) Water leaks often account for a large part of lost revenue in water utility systems. Strategies and technologies to pinpoint leaks include water balance (to compare submeter to master meter  usage),  field  observations, and listening devices (effectiveness related to pipe material, installation depth, soil type). Preventive maintenance (monitoring water mains for leaks) can pay for itself but often is provided at little or no cost by utilities. (3) Periodic water main flushing (three times a year to once every 3 years, based on system age, configuration, and condition) via system fire hydrants removes impurities (e.g., rust, slime growth, tuberculation, sediment deposition) and improves flow; distribution system areas with dead legs or low water use might need more frequent flushing. System-wide flushing has specific goals, can take weeks, is as unidirectional as possible, and requires planning and coordination (e.g., system user notification, special notification and coordination with sensitive users, wholesale supplier coordination, crew equipment preparation, dechlorination compliance, advance mapping of each area and valve closures).

Operations and Maintenance

Disinfection. Water mains are disinfected according to the AWWA standard (C651-05), which allows three options for superchlorinating pipes and fittings: continuous feed, tablet (most common), and slug feed.

Complaints.  All customer complaints (via phone, e- mail, in person) must be addressed seriously and promptly and tracked via a formal procedure. The system operator must take time to interview customers and understand their concerns, which must be investigated to determine whether water quality poses a health threat (e.g., interviews, water sampling, flushing, periodic visual observations, drawing reviews). Follow- up work depends on the nature and cause of poor water quality. Utilities mapping can have a layer for complaint locations, types, and dates to identify patterns.

Metering. Depending on water cost, metered data to at least building level helps compare master meters to identify distribution system leaks, but data must be regularly read and logged (sometimes with utility company help). Some universities use real-time metering, which provides feedback and has alarm levels to quickly pinpoint problems but must be managed by staffs that can be too busy to set up, maintain, and monitor such systems. At least eight types of meters (listed, depending on flow range and pipe size) measure and display water passing a given system point; AWWA standards for each note required characteristics for use in water distribution systems. Meters must be properly installed and checked periodically (every 1 to 4 years based on meter type and size) for accuracy.

Certified Operators. Federal drinking water regulations require each state to develop and manage an operator certification program (often with different levels and operator types, each with specific requirements and tests). A certified operator must supervise each public water system (e.g., O&M, sampling, record keeping, troubleshooting, public relations, safety, administration). States must keep a register of qualified operators. Testing registration and scheduling can take a long time.

Figure 3.17. Approved testable reduced pressure backflow prevention (BFP) devices (two in parallel to avoid disruption of water supply to building during annual testing).

Emergency Preparedness. Water system managers must plan to minimize effects of threats and disasters (e.g., earthquakes, floods, fires, tornadoes, extreme weather, terrorism, power outages). The most critical water distribution system elements during a disaster include storage, pumping, and safe drinking water delivery from other sources (with special issues in earthquake zones). Most schools have emergency operations plans with tabletop exercises, plan updates, and maps on water storage and distribution; at a minimum, plans include vulnerability assessment results, contact information and organization charts (internal and external), plan to recover operations, and communications procedures for the media and public. Water system integrity before and during a disaster must be evaluated (e.g., with tools such as early detection and warning via real-time distribution system monitoring; emergency sampling kits).

Cross-Connection Control.  Water  suppliers  must ensure safe drinking water and often minimize the risk of cross-connection (nonpotable water entering the potable water system), usually because of backflow events (backpressure or backsiphonage). Backflow prevention device types are vacuum breakers, double check valve assemblies, reduced pressure backflow assemblies, and air gaps; the required type depends on potential hazard and risk (e.g., see local water supplier or AWWA (American Water Works Association) manual M14. Some high-risk buildings use separate potable and nonpotable systems. Backflow protection requires significant and costly staff O&M time and testing by certified testers (often in house on large campuses); the risk of continuous dumps from reduced pressure devices must be addressed (see Figure 3.17).

Reclaimed Water

Reclaimed water and gray water used in irrigation, toilet flushing, fire protection systems, and saltwater intrusion barriers are still limited in some states. Dual systems can be used per IPC requirements (e.g., purple piping). Water reuse in some areas is limited by water rights, public perceptions, and pathogen exposure concerns. All water reuse can decrease potable water volumes and treatment costs, thus benefitting the region, and in the long term, adding value for universities expected to lead by example (if not profit directly).

Small Systems

Water system size and source dictate treatment type (e.g., disinfection, filtration, sedimentation, ultrafiltration, reverse osmosis). A small system has fewer sampling and analysis requirements than a large one but still must be managed (e.g., regulatory compliance, water resources, treatment, distribution, personnel). Most violations relate to coliform sampling and data evaluation (e.g., monitoring frequency noncompliance, incorrect data calculations). A key element is planning (e.g., for regulatory compliance, trained personnel funding, system O&M, capital improvements, infrastructure repair, disaster response). In-place plans (e.g., monitoring, master, capital improvement, and 10-year financial plans) must be regularly updated. Most state environmental agencies designate representatives to assist small systems.

Regulations

Drinking water is regulated under the Safe Drinking Water Act of 1974 and amendments. Most states hold primary environmental enforcement authority (and often follow federal regulations). (1) Legally enforceable EPA contaminant standards set maximum contaminant levels (MCLs) in six categories (microorganisms, disinfectants, disinfection products, inorganic chemicals, organic chemicals, radionuclides). Maximum contaminant level goals (MCLGs) are nonenforceable (no known or expected health risk below them). Most primary drinking water contaminants have an established MCL and a lower MCLG. Secondary standard guidelines for contaminants that can cause cosmetic effects (e.g., skin or tooth discoloration, aesthetic effects) are nonenforceable. (2) Monitoring requirements depend on source water, population served, and system type (transient or nontransient); regulations describe analysis types, frequency, and number of samples. Monitoring plans specify analytical methods for certified laboratories to perform. (3) Reporting requirements include analytical reports and consumer notification of a violation (by severity) and annual consumer confidence reports.

Record keeping requirements are specified for data collected during system monitoring. (4) Federal and state regulations set treatment requirements and filtration use criteria in lieu of MCLs (e.g., for lead and copper). (5) Residual disinfectant concentrations for filtered systems are specified at the entrance to (and in) the distribution system and by chlorine MCL. Disinfectant residuals and byproducts can form after a disinfectant (e.g., chlorine) reacts with naturally occurring materials in the water.