The Colorado River in the Grand Canyon. Source fotolia.

+ Urban planners must take water availability into account when considering new developments.

Six of the ten largest US cities are located in the arid southwest region. Would that be the case if water availability had influenced land use planning a century ago? The predicted scale of future urban growth means that land use planning and regional growth plans simply must consider where people’s water will come from.

Keeping up with global urban growth projections for 2030 will mean developing an area the equivalent of 20,000 American Football fields a day between now and 2030. And it’s estimated that accommodating the water demands of this growth will take the equivalent of 20 Nile Rivers. We have to think about where this water will come from and plan accordingly.

Traditionally, growth has been based on economic activity, business and industrial opportunities, education, transport and commerce. But now water availability needs to drive how and where cities grow. Otherwise tension will arise between nations (or within nations). We could see water wars or, in the worst case, cities may not have enough clean water to supply their residents.

Factoring in water availability could significantly change the shape of urban developments – as was the case on a recent Arup project in Asia I worked on. The town was in a region that received just four inches of rain annually. If water were supplied only from nearby aquifers, this reduced the population projection by 20%. To meet the original population projections, water would need to be transported significant distances, increasing costs and energy consumption.

So how can we ensure that new developments take account of water availability? And who will police what is built where? In the US, Arizona brought in regulations to address the problem. The Arizona Department of Water Resources has created the Assured and Adequate Water Supply Program to preserve groundwater resources and promote long-term water supply planning.

Before selling parcels of land, developers in Arizona must show that their project meets criteria including: physical water availability, legal water availability, continuous water availability, financial capability and water quality. The Arizona Department of Real Estate will not issue a public report, which allows the developer to build and sell housing lots, without this.

More widely, governments under pressure to build will be tempted to build first and work out how to supply water later. But this is unsustainable because transporting and distributing water requires significant energy. For example, delivering water to residents of Southern California accounts for 33% of the total household energy use in Southern California. [Source: Energy Down the Drain].

The link between water and city planning is clearly a big issue, not only for the US but for the entire world; for developing nations growing at an unprecedented rate and older less growth-full nation states. Perhaps the rest of the world can learn from the current state of water supply challenges in the US and be informed in their current and future planning process. For example, all regional planning authorities could exercise and enforce prescriptive water availability planning policies similar to the Arizona Department of Water Resources model.

And maybe, given the imperative of water to humanity, we need a global authority to influence where urbanisation and development should occur based on water availability. That authority would need to trickle down to each nation, which would then evaluate which areas are resource-rich and develop their long-term plans.

Water cannot be the sole driver in urban planning, but it needs to be a large part of the equation if we’re to create sustainable cities.