Palo Alto resident Keith Bennett estimates that you can quench the thirst of Palo Alto's entire daytime population for a year with all the water that was pumped out of eight residential properties last year to construct basements.

For Bennett and his growing grassroots group, that's a problem that the city isn't tackling with enough gusto. Next week, as the City Council prepares to consider new regulations for "dewatering" -- the practice of pumping out groundwater -- he and others members of Save Palo Alto's Groundwater plan to lead the call for action.

The group, which sprung up in 2015, can already claim some success. Two years ago, the council began requiring that dewatering sites provide "fill" stations, which allow water otherwise headed for the storm drains to be recaptured and used for other means, including irrigation and construction cleanup. And in early 2016, the city strengthened the fill-station requirement, mandating that these stations have enough water pressure to accommodate multiple users drawing from them at once. The council also began requiring builders to submit studies showing how their projects affect nearby trees, landscaping and buildings.

On March 7, the council is preparing to go even further. One proposed change would require stations to be capable of filling a truck in 10 minutes, which must be demonstrated before any dewatering can proceed, and to be designed such that the storage tank would always be at least one-half full.

Another requirement would limit pumping to 10 weeks (in addition to the two-week "startup period," during which time the builder would have to demonstrate compliance with water-quality standards). A builder would also be prohibited from digging out more than 3 feet below the basement floor during the startup period. Once the basement slab is poured, the depth would have to be 1 foot. Further, the property owner would have to offer to water trees and plants on adjacent properties if requested; to report all measurements on a bi-weekly basis; and to submit a geotechnical study based on pumping tests at wells on the site.

While these rules would take effect in this spring (pumping is only allowed between April and October), the council is also eyeing more substantial steps in 2018. The city may start requiring builders to rely on "cutoff walls" for basement construction -- a technique that limits pumping to a more contained area and that generally is more expensive.

The new regulations have already received the endorsement of the council's Policy and Services Committee, which approved them in December after hearing from dozens of residents, many wearing "Save Palo Alto's Groundwater" buttons. Bennett posited at the meeting that it's not unreasonable to asks developers to pay a little more to avoid wasting a public resource.

"Our aquifer is a precious shared resource, which Palo Alto has the responsibility to protect," Bennett said. "A significant amount of the community's groundwater is pumped and dumped. This is neither acceptable to the community nor sustainable."

Bennett has plenty of allies in his battle to preserve groundwater. Esther Nigenda, also a member of the grassroots group, recently penned a letter to the council listing the various reasons why her group opposes dewatering. The practice, she wrote, is environmentally unsound and is equivalent to a "localized drought," with impacts to properties hundreds of feet away. She also argued that less than 1 percent of the pumped water comes from the property being dewatered; the rest comes from neighboring properties.

"Residents want to know why they should conserve water (on their properties) when they see water gushing down their (storm) drains," Nigenda wrote.

While her group has in the past called for dramatic measures, including a moratorium on groundwater pumping and a per-gallon fee for pumped water, Palo Alto officials have opted for a more gradual approach. This generally involves tweaking existing rules, adding relatively modest regulations, monitoring impacts and making revisions based on experiences.

Last year, according to Public Works staff, the city's eight projects pumped out 140 million gallons (the city as a whole uses about 8 million gallons per day). In several cases, the applicants submitted geotechnical studies that predicted lower flow rates than occurred. This prompted the new requirement that the measurements be based on actual wells, rather than projections. The proposed rules also addressed a concern from some residents that the fill stations have inadequate flow rates.

A bigger change may be on the way in 2018, when the city may abolish the existing groundwater-pumping methods (known as "broad area dewatering") and require "localized" techniques that require less pumping. Last year, Bennett began working with local architect Daniel Garber to discuss the benefits and added costs of localized construction, which separates the basement from the rest of the area with a cutoff wall and only pumps from within the wall.

Garber himself plans to do projects this year that will use a localized-dewatering technique known as "secant shoring." The process calls for boring holes to create an underground wall without excavating the soil. The wall is formed by mixing the earth with a weak cement or clay, according to Garber.

In December, Garber argued that one way to incentivize the localized approach to dewatering is by waiving the requirement for the type of enhanced geotechnical study that those who do broad-based pumping would have to conduct. The enhanced study, Garber said, costs more than twice as much as a standard geotechnical study, which all applicants would still be required to conduct.

Last week, Garber submitted a letter outlining several other advantages of the secant-wall strategy. According to Garber, it takes about half the time to build the wall than to pursue the broad-area dewatering; and unlike the broad-area method, it can be done any time during the year.

"The homeowner isn't restricted to just the non-rainy season to build because the City's storm drain system isn't burdened by the large amounts of water that results from a project that utilizes broad-area dewatering methods," Garber wrote. "Thus, localized dewatering strategies add flexibility to a homeowner's construction schedule, adds only a very small percent to the overall cost of any new house and importantly avoids removing millions of gallons of water from our underground aquifer."