I get a lot of my best ideas while brushing my teeth. This morning, as I watched the water swirl down the drain, I suddenly thought about how much expensively-heated water gets wasted every day from shower stalls around the world. And then I thought about penguins and camels. Because they both have an arrangement of blood vessels in their lower legs that act as a heat exchange mechanism. So, in the case of the penguin, warm blood going to the feet is cooled by cold blood coming up from the feet, meaning that they lose much less heat out of their feet than we would. In camels, the same principle works in reverse: relatively cool blood from the body is heated by hot blood from the feet (ever walked barefoot in the desert in summer? Pretty damn hot), which helps them maintain a comfortable body temperature.
So, why not install heat exchangers in the waste pipes? Water from the bathroom and kitchen drains could go through a heat-exchanger, warming up the water that is going to the boiler to be heated. That should save quite a bit of energy. Yay! Global warming solved.
Or not.
Sure, on the surface, my idea might have merit. There may even be a billion dollar company in it. But here are some of the hurdles to cross.
1) would it actually work? In theory, yes. Of course. But would it actually save enough energy to be cost efficient? In other words:
2) is it a solution to a problem, or a solution looking for one? Do houses actually lose that much heat through their drains? There may be all sorts of reasons why they don’t.
3) has it already been done? I would bet a million dollars if I had them that something like this is already being done in large scale industrial contexts, like power stations.
4) can my penguin-foot units be retro-fitted to existing houses, or could it only be done on new-builds, which tend to be much more energy efficient anyway?
5) I’m sure the engineering costs of developing this would be considerable, because the unit would have to be quite cheap to produce. It’s a basic rule of life that simple, reliable solutions are harder to develop than complicated ones. Because they have to be just right in every detail. Would sales justify the costs?
6) Then having done my feasibility studies, and gotten the prototypes developed, we then have to actually sell the damn things. To whom? Home owners, home builders, environmentally conscious people? (Better not be building the units out of high impact materials; let’s double the budget for development…)
So here’s my point: ideas are ten-a-penny. I like my penguin-foot bathroom drain heat exchanger. But I’m not willing to mortgage my house, and work 12 hour days for three years, to develop it. I don’t like it enough.
Because at the end of the day, ideas are cheap. It’s execution that matters.

[Update: somebody beat me to it anyway: you can actually buy a drain water heat exchanger! https://ecodrain.ca/en/ Thanks to Jeremy B. for letting me know.]
Which brings me on to my thought for the day. Give away all your best ideas. If you want to make my idea real, go ahead, it’s yours.
I first came across this concept, of giving away all your best ideas, in a book which is in a box at home. I’ll dig out the reference when I get back. But in the meantime, I suggest let ideas come as they may, and put 100% of all efforts into execution.
Speaking of which; I’m technically on holiday. But, the layouts for my book Swordfighting are right now on my iPad waiting for me to check them for errors… so I’d better follow my own advice and get on with that! Because any damn fool can get the idea for a book. But to write a book, that’s harder. And getting it finished, edited, laid out, and published, is harder still.