Everyone Wants to Reuse Their Water. Here Is the Arithmetic Nobody Does First.

In March the DENR put a number on it: around 200 billion pesos to fix the country's water problem, with roughly 40 million Filipinos still drawing from sources nobody would call safe. Here in Cebu we did not need the press release. We have been living the shortage since summer.

Every time that news runs, my inbox changes shape. Facility managers, hotel engineers, plant owners, all asking a version of the same question: sir, can we not just reuse our own wastewater?

Yes. Technically, almost always yes. I have built the trains that do it. But in thirteen years I have watched more reuse projects die on a spreadsheet than on an engineering drawing, and I would rather tell you where they die before you spend money finding out.

Reuse is not a treatment problem. It is a demand problem.

The first thing I ask is not what technology you want. It is this: what would you actually do with the water, and how many cubic metres of it per day?

Almost nobody can answer that on the first call. And it is the whole project.

I worked on a hospital in the Visayas producing around 250 cubic metres a day of treated effluent. Big plant, good numbers, water going out clean. The owner wanted reuse. So we sat down and counted what the building could legally and safely take reclaimed water for: toilet flushing, cooling tower make-up, landscape irrigation, floor and grounds washing. Not laundry, not sterile services, not anything touching a patient.

The honest total came to a fraction of what the plant was producing. So the question stopped being "can we treat it to reuse quality" and became "is it worth building a polishing train and a whole second water network for that fraction". That is a much better question, and it is arithmetic, not engineering.

If your non-potable demand is small, reuse is a slogan, not a project.

The second pipe costs more than the plant

This is the part that surprises owners. Upgrading a treatment plant so its output is fit for flushing and irrigation is often the cheap half. What costs money is everything after the plant: a storage tank, a booster set, a completely separate distribution line running to every fixture you intend to feed, colour-coded and physically isolated so nobody can ever cross-connect it to the drinking line, plus the signage and the discipline to keep it that way for twenty years.

In a building that is still on paper, that second line is almost free. You are only adding pipe to a job that is already trenching and chasing walls.

In a building that is already operating, you are chipping through finished floors and shutting down wings to do it, and the reuse project quietly becomes a renovation project. I have seen the number triple between those two situations for the same volume of water.

So when a client tells me they are interested in reuse "someday", my honest advice is either do the pipework now while the walls are open, or accept that someday will be expensive. There is no cheap retrofit version of a parallel water network.

Do the cost per cubic metre before you fall in love with the technology

The only number I care about at this stage is what a cubic metre of reclaimed water will cost you to produce, all in, and how that compares to what you currently pay for water from the tap or the tanker.

A well-run biological plant, the fixed-film kind we normally build, sits in the region of 29 pesos per cubic metre to operate. Push that same water through an advanced oxidation route with ozone and disinfection and you are looking at something closer to 90 pesos per cubic metre. Those are our own operating figures, not brochure figures, and they move with your power tariff and your loading. You can put your own flow into the estimator and see where you land.

Now put your water bill beside that. In a lot of Philippine locations, piped water is still cheaper per cubic metre than the polishing train needed to make effluent safe for reuse. When that is true, reuse is not a savings project.

But it can still be the right project. Because there is a second case, and it is the one that is actually driving the calls I get this year: supply security. If your operation stops when the water stops, then the question is no longer what a cubic metre costs. It is what an hour of downtime costs. A hotel that cannot flush, a food plant that cannot wash down, a laundry that cannot run — for those, reclaimed water is not a discount. It is a spare tyre.

Those are two completely different business cases and they justify two completely different budgets. Decide which one you are in before you ask anyone for a quotation, because a supplier who does not know which one you are in will sell you the wrong plant.

Where reuse has genuinely paid, in my own jobs

Wash-down and vehicle washing, when the volume is real. On a commercial building we looked at recently, a closed-loop recycle for the wash bay only made financial sense above roughly 10 cubic metres a day of washing. Below that, the cheaper answer was to pre-treat the wash water and let the main plant absorb it. We put both in the proposal with the crossover point written down, and the client chose with their eyes open.

Cooling tower make-up. Steady, large, unglamorous, and non-potable by nature. This is usually the single best reuse target in a commercial building, and it is the one most people forget while they are arguing about drinking water. On that argument, my honest answer is here.

Irrigation and grounds. Reliable demand, forgiving quality requirements, and it visibly survives a dry spell when everything around it browns out. Owners underestimate how much goodwill this buys them.

And the case people never expect: sites where reuse is not about saving money at all, but about being allowed to operate. No sewer connection, no acceptable discharge point, a receiving creek the neighbours already complain about. On those sites, reusing the water internally is the only way the numbers work at the permit level. That is a legitimate reason to build it and I have designed for exactly that.

If you ever want reuse, stop mixing your streams

My first serious project was a food processing plant — hams, hotdogs, beef jerky. Two mistakes I still teach from. I underestimated the emulsified fats and oils, and I specified a grease interceptor where that stream needed dissolved air flotation. And the domestic wastewater and the process wastewater had been combined into a single line, which pushed the whole plant into stricter compliance parameters than either stream would have faced on its own. I have written that one out in full.

We stabilised it by retrofitting fixed-film media into the aeration tank, and I did not bill that client again until the plant passed and stayed passing. We were on that site at all hours, holidays included. Their previous contractor had walked off after collecting ninety per cent of the money, so I was rebuilding trust that somebody else had broken.

Here is why that story belongs in a piece about reuse. The moment you combine a clean stream with a difficult one, you have to treat all of it to the standard of the worst of it. Reuse dies right there, on a plumbing decision made years before anyone said the word reuse.

Cooling tower blowdown, rinse water, condensate, roof rainwater — these are nearly-clean streams. Send them down the same pipe as the kitchen and the toilets and you have converted cheap water into expensive water, permanently. If reuse is anywhere in your ten-year thinking, segregation is the decision that keeps the door open, and it costs almost nothing to do at the start.

Where I say no

Landfill leachate. We design and build leachate plants, and people ask whether the treated leachate can be reused on site. You can get there. Ammonia, chloride, dissolved solids and metals will all come along for the ride, and removing them properly means membranes and the concentrate stream that comes with them. The cost per cubic metre lands somewhere no operator will accept, and the reuse demand on a landfill is small anyway. I would rather tell a client that before the design fee than after.

The general rule I use: reuse the streams that are already close to fit for purpose. Do not build a monument to purify the one stream that fights you hardest.

And on the scarcity debate itself

I want to say something that is not popular in this industry.

Treated effluent discharged to a creek is not wasted water. It goes back into the same basin the country draws from. When we talk as if every cubic metre discharged is a cubic metre lost, we are selling a feeling, not a fact.

The genuine losses are elsewhere: untreated discharge that makes a receiving water unusable for everyone downstream, distribution losses in the network, and groundwater drawn faster than it recharges. In coastal Cebu that last one has a specific consequence — pull too hard and the aquifer takes in seawater, and once chloride is in a well, no amount of good intentions gets it out.

So the strongest argument for reuse in the Philippines, to me, is not that it creates water. It cannot. It is that it takes large users off the potable supply and off the aquifer, and leaves that water for the households that currently have none. That is a real, defensible reason to spend the money, and it survives scrutiny in a way that "we recycle our water" on a sustainability page does not.

Before you spend a peso

1. Write down, in cubic metres per day, your actual non-potable demand — flushing, cooling, irrigation, washing. Measure it if you can. Do not estimate it upward.
2. Find out what a cubic metre of water costs you today, including tanker deliveries during a shortage. That is your comparison number.
3. Decide honestly whether you are buying savings or buying supply security. They justify different budgets.
4. Ask whether your streams are segregated. If they are not, ask what it would cost to separate the clean ones now, before anything else is designed.
5. Then, and only then, talk to a supplier about technology.

A reuse system that cannot survive those five lines on a piece of paper will not survive its second year in a plant room.

If you are working through this for your own site and want a straight answer on whether the numbers work, send them over. We are one of the few wastewater companies in the Philippines that will tell you when reuse is not worth building. Book a free 15-minute consultation and bring your water bill.