The city Board of Water Supply is offering up its sprawling main base of operations in Honolulu for lease and redevelopment in a move to earn income that helps pay for agency expenses and possibly reduces customer costs.

The agency Friday issued a request for proposals to redevelop 5.75 acres of land that includes its headquarters building, an engineering building and parking lots on South Beretania Street near the state Capitol.

A 65-year lease is being presented for the land, and a developer would pay the agency rent for the property and provide replacement space at no cost. A winning bidder also would have to pay a one-time contract fee of $1 million.

"We are evaluating the potential for our Beretania property to generate lease revenue to help pay for the operational and capital improvements needs of the water system,"Duane Miyashiro, the board’s chairman, said in a statement. "However, any proposed development must prove to be economically beneficial to the BWS and the customers we serve before we pursue it."

Bids are due June 12. A short list of preferred proposals will be assembled in August, if needed, and a selection could be made next year, according to the bid documents.

It’s hard to anticipate what kinds of plans developers might propose for the site.

The property’s zoning allows medium-density apartment use with a height limit of 100 feet, though a developer could seek a zoning change from the city.

Roughly half the property is used for parking — close to 400 stalls for staff, customers and equipment vehicles, which creates much of the potential for redevelopment.

Under the bid offer, the property would have to be developed without interrupting the agency’s operations.

About 345 people work at the Beretania property, which includes a customer service center, administrative offices and microbiology and chemical testing laboratories.

A building that houses a pump station built in 1926 would remain and is not part of the development plan.

The three-story public service building and a four-story engineering building might be left as they are for agency use, converted for new use or demolished and replaced with other structures.

However, bid documents say that the State Historic Preservation Division opposes major changes or demolition of the public service building, which is considered eligible for listing on the National Register of Historic Places along with the engineering building.

The engineering building was built in 1939 and designed by Hart Wood, a junior partner of famed Hawaii architect Charles W. Dickey who later established his own practice and designed many of Honolulu’s water pump stations that have been recognized for national awards.

The bid documents say the engineering building, which is notable for a green slate bas-relief sculpture by Honolulu artist Margarite Blasingame at the entry, represents one of Wood’s earliest, simplest and clearest uses of modernist design.

The public service building also was designed by Wood, though he died before the building was completed in 1958.

According to the bid documents, this building combines "quintessential modernist design icons" such as a brise-soleil, or sun screen grille, with Asian-influenced elements that include a main entry canopy representing a Japanese torii, or shrine gate, and exterior walls with a Chinese-inspired fretwork of gridded louvers.

The building is connected to the engineering building by an arching pedestrian bridge, and has a street-front water fountain featuring the inscription "Uwe Ka Lani Ola ka Honua," which means "when the heavens weep, the earth lives."

A developer will need to consult with the historic preservation division to determine whether demolition, partial demolition or extensive renovation is allowed for either the public service building or engineering building, the bid documents say.

Other interesting aspects of the property include a cap-rock well in the basement of the public service building and a bomb shelter system with tunnels in front of the engineering building.

Because the property was once used for habitation by ancient Hawaiians, a report commissioned from Cultural Surveys Hawaii Inc. concludes that there is a high probability that the site contains pre-contact and 18th- and 19th-century burials and cultural deposits. The agency recommends archaeological monitoring of any deep ground-disturbance work.

An environmental assessment and possibly an environmental impact statement will also be required.

Because the property is within the Hawaii Capitol Special District, a special district permit may be required for redevelopment.