Build a toilet flusher that uses rainwater that you collect on the roof of your house. An idea from Bart

Inspired by the 'don't use toilet paper idea'. You'll have to get permission of the house owner, but for the rest it is not very complicated.

I would love to have this in my house!

Me too!! @bart, do you have any links with construction tips? Or how you would set this up?

I know a guy who has the installation. It's basically a big tank, with a overflow protection, for when the tank is full. And the tank is connected to the reservoir in your toilet. I'll try to find more info on this. The difficult part is finding a way for a pipe from the roof to the toilet. It's best done during a renovation. But if you live on the top floor, it might be easy.

This is one example, but there is a lot on the net. http://www.youtube.com/watch?v=tvIFMGuqBp8

i live on the top floor...

or....a compost toilet! they rock! but it will be pretty challenging living in the city....

@ingetje and you own the place? than you should think about it. If Maarten may not be able to do it in his house, he could 'lend' your house. This is a page which explains how to do it: http://www.reuk.co.uk/Flush-Toilet-with-Rain-Water.htm
You might want to keep the current drinking water system in place, for dry periods.

It definitely sounds like a fun idea and I really don't want to sabotage your enthusiasm. To save water in a rainy country as Holland has probably two positive effects:
1. It saves the energy to purify the used water again and
2. Maartens waterbill goes down a little

Taking about the global problem of lack of freshwater, changing your (or Maartens) habits of consumption would probably do much more. By consuming products such as coffee, milk, meat, bananas that need a lot of water to be made we are literally importing water from countries that are chronically suffering from water deficiency.

Check this infographic: http://awesome.good.is/transparency/web/trans0309walkthisway.html

nice graphic! i knew a dishwasher actually uses less water than washing dishes by hand, but the difference is big.
But what i curious about: how about comparing eggs with cereals and wine with beer on every field at the same time. So not only water, but also the energy needed for production, transport, the carbon offset, the treatment of animals, the packaging, etc.
And for this idea: i think that the best ideas on this site are the ones Maarten will be manage to execute, that actually improve something real (big or small), and that the results will inspire other people to think about what they can do.

Wow, thanks everybody! All very interesting information.

First of all I never realized that creating a rainwater/grey water system would be so easy! I'm sure it's still some work, especially when you want to integrate it in your walls or something similar, but it seems easier than I thought it would be. I'm going to check this out more to see how plausible it is to build this in my house and how I could set it up in that case.

@philipp, nice infographic!! Very informative (anyway www.good.is is an awesome website). Never knew that coffee and meat (chicken, beef) need so much water to be produced. I agree with you that a change in consumption would make a lot of difference (more then I thought before I saw the infographic). I'm also sure that you will agree with me that it's also about the little things that make a difference, so creating a rainwater system is a valid idea, and it's something we can directly change. I think that becoming more aware of the water you indirectly consume and waste would be a nice action next to this one. Supporting it.

about the rainwater system: lots of rainwater systems also connects to the washing machine for example. (It actually cleans your laundry better than drinking water, because it's not so calcified). But that kind of systems need an electric pump, to make the pressure high enough. And I even saw people make their own water cleaning system, so that they can drink that water as well. Those are complex and expensive systems. But for the toilet it's simple. I'll ask my friend (who has this system) if he has drawings or other information.

And about the infographic: the price of any product should reflect the costs that need to be made to compensate for all damage done to the world. One dutch guy once thought about creating Belasting Onttrokken Waarde (Taxes on extracted value) instead of our current system. So you pay tax on everything that you extracted from our earth that can not come back (or it takes effort to bring it back). Paying for planting trees to compensate for carbon offset is an example, but you can think of the same for the water in the graphic, and for the energy, etc... I am afraid Maarten will not succeed in changing the worlds tax systems, but it is interesting idea. Beef is simply too expensive to eat...