Land Use Choices Change Water Demand Projections

Cities across Texas are tasked with the daunting job of ensuring adequate water for their citizens into the future.  Decisions that are made regarding new supply of each can have large economic consequences for existing customers, but not pursuing supply may have dire consequences for the sustainability of the city.  Unfortunately, this fear of running out can cloud discussions about how much new water is really needed.  The key to getting this right is land use.  Too bad land use is often left out of conversations about expanding water resources.

Hopefully, the conversation will change.  Next week, I will be taking part in the San Antonio Clean Technology Forum, which will bring city leaders together to discuss critical planning questions and find a way forward. The focus of the forum is the big picture for growth in an effort to understand the relations between demand projections and new supply planning.  Simply installing infrastructure outside the city limits incentivizes sprawl and evades the planning that is really necessary for a successful, sustainable city.

Demand Projections Change with Behavior

Municipal water demand is dictated by both the residential and commercial needs of a city. Water demands are calculated based on the approved land uses within the potential service areas, coupled with the average annual daily water demand and peaking factors associated with the various land uses. Because demand projections are based on usage assumptions, they can be altered by behavior modifications.  When people use less, the overall demand needs projected over time decrease significantly, which also changes the new supply timeline.  Assuming we will use water the same way in the future as we do now is unwise.   Thankfully, there are many things that we do differently in the present as compared to the past. Technology and behavior changes continually allow us to do the same things with less.  This trend of change needs to continue.

Growth as a Driver

Along with how each user uses water, growth is ultimately the driver that defines projected resource needs. Proper management and understanding of growth is the key to any city’s success.  Certainly, diversity of water supply is important for resilience, but the quantity of supply needed to sustain growth will vary based on the expansion vision.  The need for new resources is not only defined by how much we grow but how we grow.  The challenge for cities is often finding the leadership to look at a city and its needs as an integrated whole.

The Texas Water Development Board predicts that South Central Texas will grow by 75% between 2010 and 2060.  Municipal water use is one of fastest growing water categories.  For example, San Antonio Water Systems’ (SAWS) Land Use Assumptions Plan predict that the population of their service area will increase by approximately 230,000 people in the next ten years.   This translates to almost 100,000 household units, each of which will need approximately 300 gallons of water per day excluding the water required to provide energy to these same homes. The total number of gallons needed depends on how a city grows not whether it grows.

A change in land use requirements can result in an increase or decrease in anticipated demand.  In many instances, a city’s projected water demand is driven by developments in undeveloped areas within the city limits and assumed growth in the extra territorial jurisdiction (ETJ).  Studies show that new homes require considerably more water than older homes as a result of the systematic installation of irrigation systems in many new housing developments.  Larger lot sizes and houses with greater footprints can also increase overall usage.

Planning for Peak

There is another supply driver that must be examined: peak usage. Most water supply forecasts models are primarily concerned with ensuring service for limited peak demand times of the year when usage spikes and maximum supply is needed.  This means that for most of the year we have plenty of water for our needs, but for small snippets of the year our needs increase due to outside influences.  Many times, cities plan expensive supply measures to ensure that peak is covered.  In Texas, this peak occurs in the summer when air conditioners are cranking and lawn watering increases substantially.  New supply measures may be avoided or significantly postponed by simply reducing demand peak usage.

What to do?

Two primary strategies can be employed by water utility managers to balance increasing water demand and supply in the urban sector:

(1) Develop land in way that use less water per capita

(2) Decrease peak water needs

Cities can control demand management through implementation of conservation and efficiency measures. In addition to the suite of incentive and rebate programs offered by both the water and electric utilities, demand can also be managed through city ordinances such as efficiency oriented building codes. Land use limits are also tools that can be used to minimize demand while still allowing for growth.  Examples of effective land use initiatives include encouraging high-density growth near the urban core and dictating water efficient landscaping and energy efficient construction for new builds.

Controlling water intensive landscaping is particularly important because outdoor watering can account for 30-50% of the city’s total withdrawals, particularly in the summer months when water is scarcer. Houses with irrigation systems can more than double a household’s water use as compared to houses that do not have one. Requiring installation of irrigation systems often provides a disincentive to plant drought resistant plants in new communities and increases demand more than if the same communities were planned differently.  This means that it is not necessarily the growth itself that causes the challenge; it is growth without the appropriate guidelines. Reducing discretionary watering will the biggest impact in the peak months and reduce need for new supply.

The success of a city depends on a master plan that includes all aspects of planning including water and energy needs within a land use context.  A city cannot predict demand of resources before first determining who it will service, which is dependent on land use decisions.  Expensive water purchases that can have negative environmental consequences should not be made before future demand is fully understood. The need for a big picture plan and supply decisions are not in conflict with one another, but they do necessitate initiative and vision to move forward in an effective and timely manner.  Let’s start talking about it.

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The Texas Living Waters Project is transforming the way we manage water so there will be enough for our wildlife, our economy, and our kids. Forever.

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