“Well,” he said shortly, “we can test a water sample for all sorts of things: pH, dissolved oxygen, temperature, turbidity, salinity, nitrogen, ammonia, arsenic, bacteria… Then there’s water hardness, tests for various inorganic constituents such as iron, manganese, and sulfates, as well as tests for various water pollutants. So testing, yeah, we can do that.”

“Good, good,” Mac said encouragingly.

“Just one hitch, though.” Knowles spread his hands in a helpless gesture. “We’re not out in the field, and you can’t do squat with six drops of water.”

Mac raised a startled brow. He glanced at Kimberly, who shrugged. “At least we brought you water,” she commented. “We only gave Ray a picture of a leaf.”

“Damn right. And I did good,” Ray boasted. “So don’t you ruin our track record now, Knowles. We keep this up, and maybe we can get our own TV show. You know, Law and Order: U.S. Geological Survey Unit. Think of the chicks, Brian. Think of the chicks.”

Knowles, however, didn’t appear convinced. He leaned back in his desk chair and locked his hands behind his head. “Look, I’m just being practical here. To get accurate results from any sort of water test, you need to be at the source, looking at the sample in situ. The minute you bottled up this water, a couple of things happened. One, you changed the temperature. Two, you removed it from its oxygen source, rendering a test for diffused oxygen useless. Three, the pH is going up from off-gas. Four, you may have contaminated the sample from the container itself, and five… Well, hell, I can’t think of five at the moment, but let’s just agree it’s not good. Whatever I do to this sucker, the results are about as meaningful as a sixth toe-gives you something to look at, but doesn’t do a damn thing.”

“But we don’t have a source,” Mac reminded him curtly. “That’s the whole damn point. This sample is what we’ve been given, the source is what we gotta find. Come on, surely there’s something you can do.”

Mac stared at the man with mute appeal. After another moment, Knowles caved with a sigh. “It won’t be accurate,” he warned.

“At this point, we’ll take an educated guess.”

“I don’t know if I’d even call it that.” But Knowles was fingering the glass tube bearing their precious sample. “You’re sure you don’t have more? I’d prefer about forty milliliters.”

“The best I could do would be six more drops.”

Knowles blinked. “Damn, whoever gave you this was definitely feeling stingy.”

“He likes a challenge.”

“No kidding. I don’t suppose you’re gonna tell me anything more about this case.”

“Nope.”

“Ah well, never hurts to ask.” Knowles sighed again, sat up in his chair and stared intently at the sample. “Okay. It’s possible to test for salinity. We just need enough water to cover the end of the probe. I could do pH, which also uses a meter. Of course, the probe on the pH meter can deposit a tiny amount of potassium chloride in a sample, raising the electrical conductivity and screwing the salinity test… So we do salinity first, I guess, then examine pH. As for mineral testing… Hell, I don’t know if any of our test equipment is even calibrated for a sample this small. Bacteria tests… You have to run the water through a sieve, not sure that would do much here. Same with testing for plant matter.” He looked up. “Salinity and pH it is then, though I’m telling you now, the sample size is too limited, the methodology flawed, and all the results will be too relative to draw any sort of accurate conclusions. Other than that, what the hell, I’m game. I’ve never worked a murder case before.”

“Any information is helpful,” Mac said grimly.

Knowles opened a drawer. He pulled out a small plastic box with a well-worn label that read Field Kit. He popped open the container and started pulling out handheld meters complete with long metal probes. “Salinity first,” he murmured to himself, fiddled around, then stuck the probe in the water.

He didn’t say anything right away. Just grunted a few times.

“What does a salinity test measure?” Kimberly asked. “If it’s freshwater or salt water?”

“It can.” Knowles glanced up at her. “Basically, I’m measuring the amount of microsiemens per centimeter in the water, which gives me an idea of the dissolved content. Water on its own has no electrical conductivity. But water that has a lot of salt or other dissolved minerals in it will have a higher level of conductivity. More microsiemens per centimeter. So, in a roundabout way, we’re trying to tell where this water has been.”

He looked at the meter, then pulled the probe from the sample. “All right. According to my handy dandy salinity meter, this water has a reading of fifteen thousand microsiemens per centimeter. So, bearing in mind all my earlier caveats, what does that tell us?”

They all looked at him blankly, and he generously filled in. “The water has good conductivity. Not high enough to be salt water, but there’s a fair amount of dissolved content in this sample. Maybe minerals or ions. Something that conducts electricity better than water alone.”

“The water is contaminated?” Mac asked hesitantly.

“The water is high in dissolved content,” Knowles reiterated stubbornly. “At this moment, we can’t conclude anything more than that. Now, the logical thing would be to run tests for various minerals, which might answer your question. But we can’t do that, so let’s try pH.”

He set aside the first meter and inserted a second. He watched the meter, then frowned at it, then pulled out the tip and muttered, “Goddamn probe. Hang on a sec.”

He wiped the tip. Blew on the tip. Then gave the whole thing a small whack with his hand. With a grunt of satisfaction, he finally returned the probe to the water. The second time didn’t make him any happier.

“Well, shit on a stick, this is no good.”

“What’s wrong?” Kimberly asked.

“Sample must be too small for the probe, or my meter’s out of whack. To believe this thing, the pH is three-point-eight, and that just ain’t happening.”

This time, he banged the probe twice against the desk. Then he tried again.

“What does three-point-eight mean?” Mac asked.

“Acidic. Very acidic. Eat-holes-in-your-clothes level of acidic. Basic is a perfect seven-point-oh. Most fish and algae need at least six-point-five to survive; snails, clams, and mussels require seven-point-oh; while insects, suckers, and carp can go as low as six. So when we’re testing ponds and streams with any sort of aquatic life, generally we’re at least in the sixes. Now, in Virginia, rainfall has a pH of four-point-two to four-point-five, so pure rainwater would test low, but we know this isn’t pure rainwater thanks to the salinity test. Three-point-eight,” he was still shaking his head. “That’s ridiculous.”

He glanced at the meter again, gave a final growl of disgust, and yanked out the probe.

“What’s it saying?” Mac asked intently.

“Same garbage as before, three-point-eight. I’m sorry, but the sample has got to be too small. That’s all there is to it.”

“You’re three for three.” Kimberly spoke up quietly. “Three tests, three similar results. Maybe the water is that acidic.”

“It doesn’t make any sense, especially when you consider that any pH reading we’re getting now is actually higher than the original pH at the source. Frankly, we just don’t see pH readings below four-point-five. It doesn’t happen. Well, except maybe in cases of acid mine drainage.”

Mac straightened immediately. “Tell us about acid mine drainage.”

“Not much to tell. Water spills out of the mine or goes through tailings of the mine, getting contaminated as it goes. The pH ends up extremely low, possibly in the twos.”

“And that would be extremely rare? Something unusual in this state?”

Knowles gave Mac a look. “Buddy, there aren’t many places in the world that have pH readings in the twos, let alone in the state of Virginia.”