Rain flooded off his black umbrella as Herbert Henry Oxidane, P.I., CWT, stepped outside the six-story building where he rented office space. A few minutes before, the powerhouse chief operator, Howard Clyde Muriatic, had phoned. On the third ring, the water detective answered, “Detective H₂O here. The best water treater this side of the Ohio, solving water problems drop by drop. Whatcha got?"

“Detective H₂O, we need your smarts over here at Aardvark Stamping, Inc. This is Howard. We’ve got this reverse osmosis system. My crew records a load of data on it. We just have no idea when to clean it. My guys are good with the books, see, lots of practice from their extracurricular activities, if you know what I mean. We just don’t know what to do with this RO data. When should we be cleaning the RO? We’ve been guessing. Putting our fingers in the air and just guessing.”

“I’ve been meaning to come up to your neck of the woods for a while now, Howard. I’ll jumpstart my old Ford and be over as fast as it can coast there. It’s mostly downhill,” replied Detective H₂O. “Crack open the checkbook and save me some coffee.”

* * *

Dodging the rain drops, Detective H₂O marched from the guard shack to the powerhouse at Aardvark Stamping, Inc. Their three 100,000-pound-per-hour, coal-fired, watertube boilers lined the main aisle with the operator room on the far side. As he searched for Howard, the water detective took a moment to look through the log book. Everything appeared to be in order with regular water testing and no notable events with the water treatment equipment during the last few weeks. Detective H₂O took a moment to chat with the on-floor operator he found sitting in front of the boilers with his feet propped up.

“Ox!” exclaimed Barney. “It’s been a while! How’ve you been?”

“Oh, not bad, Barney. Not bad at all. Don’t bother getting up. How about you and things around here?”

“I’d complain but nobody would listen. Things around have been going fine. We finally rebuilt some of the valves on Softener #2 a few months ago, but she’d been needing her tires kicked for an embarrassingly long time.”

“Sounds good. Is Howard around? He called about interpreting the RO data,” said Detective H₂O.

“Howard’s around here somewhere. I’ll call him on the radio and have him meet you at the RO. You’ll find the log sheets to the right of the units.”

Detective H₂O made his way to the RO, observing the flowrates, pressures, conductivities, percent recovery, temperature, runtime hours, etc. as he listened to the unit run. It was filling up the permeate storage tank, and at first glance, things looked good. The data on the log sheets only went back a month and didn’t show anything obvious. A more thorough look at the data would tell the real story though.

“Detective H₂O, thanks for coming!” said Howard. “As you can see, the RO’s humming right along. And as you can also see from that log sheet you’re holding, my crew’s good at keeping the books. We completely guess when to clean it though. The permeate flow rate is relatively constant, but I know these things do foul and need periodic cleaning. Is cleaning every three months really necessary though, or should we clean more or less frequently. I’ve got no idea.”

“I see your problem, Howard. Reverse osmosis systems are a great technology. They can save a ton of money in boiler fuel costs and water costs. I’ve worked with them for years, but they can be counterintuitive when interpreting their data. Changes in pressure, temperature, dissolved solids, percent recoveries, and so forth can make just eyeballing the data impossible. They can work against each other to make what seems like a good trend into a hidden disaster. Do you have the rest of the data? We should go back several months to see what’s been going on.”

“I’ve got better than that, Detective. I’ve been entering it into a spreadsheet. Grab that log sheet hanging there, and we’ll put that data in too.”

When Howard fired up his computer and entered the most recent data, a clear story still did not show. “Look at this, Detective. The permeate flow has been steady for the past year. Very steady. I start getting nervous when it runs for too long between cleanings. We cleaned this unit last October and then late February, but you wouldn’t know it by looking at the permeate flow. No changes at all. Are the membranes not fouling? Should I stop cleaning?”

“I wouldn’t draw that conclusion yet. Let’s see how variations in variables such as pressure and temperature affect the permeate flow. It’s called normalization and allows us to do an apples to apples comparison of the system. Would the membranes you have today perform as well under the same conditions as when they were installed? Normalization uses mathematical tricks to take the membranes back in time to answer exactly that question. We’ve been comparing apples and oranges up to this point. Let’s dump your data into this normalization spreadsheet I developed based upon ASTM standards and advice from membrane manufacturers. Then let’s see if this data sings like a canary.”

Whipping out his hand-cranked laptop from his briefcase, Detective H₂0 transferred the RO data into his normalization worksheet, copied down his equations, and updated his graphs. Then he whistled and said, “Look at what we have here, Howard.”

“Well, that’s a horse of a different color, Detective. Looks like you’ve taken the blinders off.”

“Yes,” replied Detective H₂O. “You see, as a membrane fouls, it takes more pressure to force the water through the membrane. Counterintuitively, as temperatures increase, water passes through the membrane more easily. These and other variables can make non-normalized data look just fine, but as you can see in this graph of normalized permeate flow or NPF, it doesn’t look fine at all. Look at these increases in October and late February, those would be your cleanings. RO cleanings should be done based upon an analysis of the data, like we’re doing here. Some rules of thumb of when to clean is when the NPF decreases by 10-15%, normalized pressure drop increases by 15% and/or normalized salt passage increases 10%. Some membrane manufactures may have slightly different recommendations, but these are a good place to start. Cleaning too frequently isn’t necessarily good for the membranes, just like waiting too long can be bad for them as well.”

“This is great, Detective H₂O. How have we been doing then?” inquired Howard.

“It looks like you probably waited too long between cleanings when you did the October cleaning, but the membranes appear to have recovered well. Then, when you cleaned again in late February, you probably cleaned a little too early. It may have gone another month or so before the data would indicate the optimal time to clean,” replied Detective H₂O.

“How about now? Is it time to clean now?”

“Looking at this normalized data, I’d say things are actually holding steady. Barney said you fixed up Softener #2. Was that sometime around or after the last cleaning?”

“You know, now that I think about it, yes. It was the beginning of March. That unit went prematurely hard for longer than I’m willing to admit. But should we clean the RO now? It’s been over three months, going on four. Shouldn’t we clean?” asked Barney.

“I’d say no. Clean this RO based upon the normalized data, and the data says the RO is not fouled enough to clean. I’ll leave you a copy of this normalization spreadsheet to keep logging your data into. You can email it to me periodically to take a glance over. We’ll make the decision together,” replied Detective H₂O.

“That makes me feel a lot better. The budget is tight around here at Aardvark Stamping, Inc. The longer I can go without buying new membranes the better. On the flipside, I don’t want to spend more on labor and chemicals for RO cleaning than I have too either. This is a good plan, Detective H₂O. I’m glad you’re on my side.”

“I’m always on the side of wise water decisions for both the customer and the industrial water equipment,” smirked the water detective. “Now where’s that coffee…”

* * *

In the underbelly and penthouses of the metropolis of Waterville, where the boilers percolate and cooling towers fog, there is one man who works tirelessly to end corrosion, stop scale, fight lowlife microbes, and conserve water. That man is Detective H₂O. Best water treater this side of the Ohio. Solving water problems drop by drop.