If you have got a garden, or some nice plants in your house, don't discard the water when doing a water change, use it to water your plants. You'll be absolutely amazed how well your plants to when you do this. I have enclosed a picture of my rubber plant which is 19 years old. Up until a few weeks ago, it wasn't doing much and was looking a little sorry for itself. I started watering it with tank water and the difference in its growth rate and the overall look is quite astonishing. It has suddenly started sprouting lots of new shoots and new leaves are appearing every day.
It's the nitrates you see, plants love them

It's also very beneficial to vegatable gardens too. I have read many accounts of aquarists who drop their python hose out a window to use the tank water outside. I myself am going to try routing my python hose out a second floor window so I am not putting all that water down the drain. From a second floor, the pull through that hose should be as good if not better then is created by the venturi effect of running a faucet to create the vacuum which draws water up and out of your tank.

I don't have a garden as I live in the country with too many wild animals to fend off and would require too much effort with fencing etc. Besides, there are so many local farm markets with excellent quality food at rock bottom prices all grown locally. Here in New Jersey (especially where we are, Monmouth County), I would put up our local Tomatoes and especially Corn on the Cob as the best tasting in the entire World. Corn season only lasts a couple of brief months but the sweet corn is "to die for" here. It's got to be picked and eaten the same day, but sooooooo tasty with butter ans salt...

I thought about bottling it and selling each bottle for around 10p, and then I thought, is it really worth it? You would have to prove it before people parted with their money I think. I'm not sure how well the water will work with minimum nitrates, let's say 10 or 15. The most my nitrates are at the end of the week 40, and that's only because I've got the extra Oscars at the moment.

I was toying with the idea of building a nitrate filter using plants. Problem is, it might start looking a little bit tatty and then you're stuck with it unless you want to pull it apart.

Yea but WHO would have thought 25 years ago that one of the most popular beverages today would in fact be Bottled Water, selling for about $1 a bottle and I've seen it as high as $2.50 a bottle at events where prices are generally high. You may actually be onto something there.

Of course, there is a big difference. Bottled Water is driven by peoples thirst and desire for quality water whereas Plants and more importantly "Plant Fanatics" are much much harder to find. On top of that we have many plant fertilizers out there already, easy to insert spikes etc etc. Better forget this idea......