In the early 1900s, the Raymond Basin, a huge underground water reservoir that made the development of early Pasadena possible, was overtapped and on the verge of being depleted.

Is Pasadena about to repeat the past, and this time will the precious resources of the basin fall below a safe level in the name of "emergency water conservation?"

Possibly so.

Allow us to explain why, oddly, doing something "green" such as mandating water conservation will have negative environmental impacts that need mitigating.

All across California cities are facing water-conservation restrictions. In response, Pasadena has adopted a New Comprehensive Water Conservation Plan and is about to adopt both new water policing and increased water-rate ordinances in June. But there is a flaw in Pasadena's proposed plan that could lead to its fall - it is environmentally unsustainable.

We believe that if residents seriously cut back on irrigation in their yards, there will be a profound effect on the Raymond Basin's replenishment. Simply put, not enough water will seep down from our landscaping, and well-intentioned efforts to "conserve" will backfire.

The drought affecting the Colorado River may be measured in terms of decades. Should droughts on these various sources be concurrent, the cutback in water supplies could be severe.

It's possible that the cutback could significantly exceed the 30 percent the city is currently consideringas a worst-case scenario. That would be an extremely unpleasant experience for all those downstream members of the Raymond Basin, including Alhambra, Arcadia, San Gabriel and San Marino.

We are troubled about the lack of environmental review of the impacts of the proposed conservation program on the amount of water available from the Raymond Basin, on which the city relies for 40 percent of its local water. That basin is already in a state of overdraft by Pasadena. A large portion of the allowed pumping from the basin comes mainly from the return to the water basin of water used for landscaping.

The city has made a decision that its water plan is exempt from filing an Environmental Impact Report. It's unclear whether the city has found a legitimate loophole in California's environmental law, CEQA. But if Pasadena wants to be considered a green city, it would be hypocritical to ignore such a serious environmental impact. Many times things are done in an "emergency" that may be beneficial in the short run but have long-term deleterious effects - including the paving of the Arroyo Seco channel during the Depression of the 1930s to manage floods and provide jobs.

The city plans to divert revenues from its proposed base water rate into its General Fund without a vote of the electorate. We say rate increases should go to building new groundwater recharge basins and cisterns to offset the loss of conserved water no longer recycled back into the Raymond Basin.

Wayne Lusvardi, who blogs at Pasadena Sub Rosa, and David O. Powell, a retired water engineer, are members of Citizens for Responsible Government.