No doubt many people find their eyes glazing over when die-hard opponents of the water filtration plant being built in Van Cortlandt Park voice a new complaint. "Get over it," they must say to themselves. "The fight's over. Move on."

The latest admission forced from the city Department of Environmental Protection by dogged local environmentalists, however, will affect your health and the health of our rivers and bays, not to mention your wallet.

Using the Freedom of Information law, Karen Argenti of the Jerome Park Conservancy recently discovered that the city miscalculated how much water there is under the surface in Van Cortlandt Park. It now plans to pump up to 1.2 million gallons a day out of the hole it has dug for the filtration plant for as long as the plant is in use - for all practical purposes, in other words, forever.

To understand the significance of this turn of events you have to go out in the rain.

At the Spuyten Duyvil train station when it's raining, even a little tiny bit, you will find all sorts of unpleasant things being discharged into the Harlem River through the pipe that runs under the northbound platform.

You'll see cigarette packs and gum wrappers and plastic bottles and aluminum cans carried from the streets where careless passersby have dropped them. More unpleasant still is what you won't see, dissolved in the flowing water: the antifreeze, oil, fertilizer and pesticides picked up by the rain. And least pleasant of all, the product of thousands of toilet flushes.

As little as a twentieth of an inch of rain or melting snow can overload the sewer pipes that carry both storm water and sewage to treatment plants. When that happens, instead of being treated, the polluted water in the sewers goes through discharge pipes like the one in Spuyten Duyvil that empty into the waterways that surround the city.

Now the DEP plans to add a million gallons of water each year to the burden of the Wards Island plant that serves the local sewers, so that it will overload sooner and still more sewage will be discharged into the Harlem.