Benefits of Water Modeling for Your System

So far in our blog series on hydraulic models for drinking water systems, we have discussed operational and future design benefits and the creation of the basic components that make up a hydraulic model. For the third and final installment, we will tackle the challenging, yet crucially important task of allocating water demands throughout the model. Of course, the first step is to analyze and determine what the existing water system demands are.

Carthage Water & Electric

Volume Produced and Volume Sold

Typically, water system Owners and Operators record two sets of water demand numbers. The total volume of water supplied or produced, and the total volume of water sold within a distribution system. So, which one do we use? All water distribution systems report a volume of water loss. Unfortunately, we don’t know where this water loss is occurring. It could be a series of leaks, possibly inaccurate metering, or even illegal and unmetered connections. Since we can’t predict with any accuracy where these leaks are occurring in the distribution system, it becomes more conservative to utilize the volume of water supplied or produced. If we were to allocate only the volume of water sold within a distribution system, we could be under analyzing the total volume of water moving through the system and thus over representing the available pressures.    

Now that we have established a volume of water to assign within the distribution system, we need to analyze the type of water users and where they may be located within the system. Residential users, commercial users, and industrial users all consume differing volumes of water. Efforts shall be undertaken to identify these differing volumes of water by looking at the total percentages of water used by each user category. Sometimes, this information isn’t readily accessible, in these cases, I suggest analyzing and isolating the top 5, 10, 15, or more users within a water system.

Zoning maps can be a useful tool in identifying where these various user categories physically exist in the distribution system. With water usage data categorized by the user, zoning maps allow the water modeler to easily input usage to the appropriate part(s) of the distribution system. If mapping isn’t available, it may be necessary to map the location of the largest users within the distribution system so that their water use can be accurately assigned.

Water Demand

Now that we know how much water is being produced/used and where the usage is taking place, we can assign demands to junctions or customer meters. With water models containing hundreds and even thousands of customer meters, it isn’t practical to assign a usage to each meter or junction manually. Instead, water usage for the various usage categories can be averaged and spread evenly over the customer meters and junctions within their usage areas. Several different tools within modeling software can accomplish this task, so we won’t address it here.

It’s also important to know that customer meter location and water usage data can be incorporated into GIS mapping. Typically, this is accomplished using an Advanced Metering Infrastructure (AMI) system. These systems automatically obtain water usage data from individual meters through a fixed communication network. With a correctly configured hydraulic model, these usages can be imported into a water model and applied to the correct meter with the click of a few buttons. This also makes it very easy to update water usage data within a model just as often as an Owner or Operator may want.

Now that at least one water usage alternative is configured, it may be necessary to create a different condition. As you can guess, water usage within a distribution system is ever-changing. Water usage during a hot summer day is almost always more than water use during a cold winter day. Also, water usage during peak hours (morning and evening) can be many times more than water usage during overnight hours. These varying demand conditions can be configured within a water model as an alternative that can be selected when calculating results.

“Customer meter location and water usage data can be incorporated into GIS mapping”

Calibration

It is critical at this point in the development of a hydraulic model that calibration takes place. The process of calibrating a water model begins by comparing field obtained measurements (flows and pressures) with hydraulic model output. Differences are bound to appear due to the ever-changing environment within a water distribution system (pump on/off status, water tower level, water demands, and time of the day), so a modeler needs to recognize and identify the more critical differences. With experience, adjustments to various factors (water level, demands locations, elevation adjustments, etc.) should be able to adequately calibrate the water model.

Congratulations! Now you have a working hydraulic computer model for a drinking water system. An endless stream of custom alternatives and scenarios can be configured for use. Whether you want to evaluate future demands, changes in pipe sizes, reconfiguration of pressure zones, you are only bound by imagination.