One of the country’s largest home builders hopes to construct a master-planned community of 11,750 homes, five schools, shops and restaurants in Ewa. But is there enough water on Oahu to feed the development?

That’s one of the main issues before the Hawaii Land Use Commission this week as it debates whether to allow the project to move forward.

Opponents of D.R. Horton’s Hoopili development have long argued that there just isn’t enough water to go around — the city would have to turn to desalination, an extreme and costly method of turning seawater into drinking water.

As is, the development would increase current water demand in the Ewa district by 25 percent, city data shows.

“Water is a major, major problem,” said Kioni Dudley, president of Friends of Makakilo, one of the project’s main detractors.

But the city is expected to tell the Land Use Commission this week the opposite: There is enough water for Hoopili.

The Board of Water Supply at one time seriously considered developing a desalination plant on the leeward coast based on concerns about dwindling water resources. As recently as 2009, the desalination plant was a key part of the city’s water plan for the region [pdf]. But the city now says it has found enough other water sources to push off desalination until at least 2035.

The Ewa region currently consumes 16 million gallons per day of potable water. The city now says it has identified an additional 17.6 million gallons of water per day, said Kurt Tsue, an information officer for the Board of Water Supply.

Meantime, Hoopili is expected to increase potable water demand by 4 million gallons a day, according to Lee Tokuhara, a spokeswoman for D.R. Horton. The development is expected to use 1.8 million gallons per day of non-potable water, for such things as irrigation.

Kalaeloa Desalination Plant

State and city plans to construct the $40 million Kalaeloa Desalination Plant go back more than a decade.

Honolulu-based Oceanit designed the plant and completed a federal environmental impact statement.

The cost of desalinating the water is expensive because of the energy costs involved in filtering the water, according to Ian Kitajima, Oceanit’s marketing manager.

Removing the salt also removes the water’s minerals, which then have to be replaced.

“It’s so pure it will make you sick,” he said. “It will pull the minerals from your bones.”

Despite all the work that’s been done on desalination plans, state and city officials say that Hoopili won’t be the tipping point. They say water conservation measures have helped control expected increases in demand.

“I’ve never taken it seriously because the idea that we are actually depending on it is actually a fool’s errand,” said William Tam, the deputy director for water for the Department of Land and Natural Resources. “When you have to go to desalinating you’ve run out of options.”

He said the state also had problems finding a place to dump the excess salt that desalination produces.

But that doesn’t mean all desalination plans are off the table, according to the city.

Predicting future water demands are difficult, says Barry Usagawa, Honolulu’s water resources program administrator. The 20 acres for the desalination plant were donated to the city under the condition that the plant be built. Usagawa said that the city will probably ask the federal government for an extension until 2035 to build it.

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