‘You can take it out of service, you can filter it, or you can cover it.’

Just the rumor that the Los Angeles Department of Water and Power was drawing up a plan to cover the Silver Lake Reservoir brought 300 people out for a fight last week.

Their pugnaciousness came from an old wound. About 15 years ago the DWP drained much of the lake to rebuild the compacted soil dam at its southern end. The dam had to be rebuilt to meet tougher state seismic standards adopted after the 1971 earthquake.

But the engineers for the project thought it best to move the dam back in a crescent shape an average of 450 feet and leave the remainder of the lake bed open for a future water filtration plant.

With a great uproar the residents of Silver Lake taught the department’s engineers that there was more to their public charge than making the city’s resources merely safe and rational.

Two years later the dam was rebuilt exactly where it was. The lake remains a shimmering landmark, surrounded on three sides by hills checkered with a rich collection of domestic architecture and on the fourth by the framed vista of the downtown skyline.

The beauty of this spot--and its palpable resistance to the urban rebuilding that goes on constantly around it--lend a sense of an Alpine village where man’s and nature’s designs are one.

Obviously, though, the lake is completely artificial. It’s one of the city’s five large repositories for the public drinking supply. For that reason it is off-limits to swimming, boating and fishing. It’s also subject to the designs of engineers seeking new ways to make their world safer and more rational.

And that’s what the rumor was about. Exactly how it started isn’t clear. Some attributed it to an article in The Times on the DWP’s plans to cover several of its smaller reservoirs. Another theory was that a DWP official started it inadvertently while leading a homeowner group on a tour.

By the time the Silver Lake Residents Assn. gathered its members around the crisis Thursday night in the Presbyterian Church on Hyperion Avenue, most of them seemed to have studied up enough to know that the rumor was only half true.

The DWP had no plans to cover Silver Lake. That project would be too big and costly. Instead, the department was thinking of building a filtration plant to remove bacteria and toxins from its 795 million gallons. A cover would only be needed on Ivanhoe Lake, the smaller gathering pond contiguous to the larger lake on its north shore.

The truth, however, wasn’t much more palatable than the rumor. It’s easy to see that putting a large filtration plant at one end of the lake and an aluminum lid on the other could be harmful to the Alpine illusion. The residents naturally wanted to know what a filtration plant would look like and where it would be placed.

To face their questions, the department sent Ronald McCoy, assistant chief engineer of the water division. It could have been a sacrificial mission. But McCoy, a tall, steady and self-confident figure in a gray business suit, showed the cunning of a presidential contender in shaping the debate to the psychology of his audience.

He characterized the situation as one of environmental consciousness. The Los Angeles water supply is safe, he said, as it always has been. But it could be safer.

He cited, as the basis for the DWP’s plans, federal and state clean-water regulations that are getting tougher because of the insistence of people just such as those in the crowd.

He used the Rose Bowl as an analogy to demystify the engineers’ jargon about parts per billion. The rules that the DWP expects to be adopted soon would allow no more than 20 drops of the carcinogen trihalomethane in the amount of water it would take to fill the stadium, he said.

He easily deflected one of the toughest questions: Why couldn’t the smaller reservoir also be filtered? He said it would be needed for engineering reasons to receive and hold clean water from the filtering plant.

As much as he could, McCoy hedged. Nothing will be happening soon, he said, because Silver Lake is probably years down the line on the department’s priority list.

But he left no doubt that eventually something will be done.

“You can take it out of service, you can filter it, or you can cover it,” he said. “Those are the acceptable alternatives.”

His best offer was to promise the Silver Lake residents that they can be in on planning what will be done.

“We learned our lesson the hard way,” he said. “We learn slow, but we learn good.”

That candor helped McCoy sidestep serious trauma. After the meeting broke up, he stayed to field questions from small groups.

When almost no one was left, one man found the nerve to ask what seemed the evening’s most audacious question.

He wondered if the department couldn’t build underground tanks for all the water in Silver Lake and then refill the reservoir just for appearance?

It could be done, McCoy judged, if someone would be willing to pay for it.