Rain water is really dirty....that may be why. But I guess even dirty water is better than no water when you really need it.

Wiper fluid is more thanwater, it is detergents ans other agents. And that is for summer fluid. Winter fluid i largely alcohol based.

A small filter would sort out the "dirt" - on reflection, perhaps just the windshield drainage would be enough to re-supply wiper fluid. My car takes a very concentrated "blue" liquid and uses huge amounts of water to dilute this antifreeze from like 20:1 in summer to 6:1 in winter. Then the idea would be to only have to fill the "blue" liquid from a bottle about once a year and the car would top up the rest.

Even though some people just add water to the fluid, the wiper fluid has additives to it to help clean the windshield and in the winter keep ice from forming on the windshield like classicscat said. But, if there were a way to filter the water through a system that would clean it and add the appropriate amount of additives then you would only have to add the chemicals and you would not have to do that all that often and you would not be using public water.

There are a couple of reasons you might want to check under the hood more than once a year, more than once a month even. If that is too much trouble, hire a cab.

Yes jashern, but the point is missed - 600 million cars, each consuming gallons of water from public drinking water supplies, combined with the embedded transport of mixed coolant travelling global supply chains; is a huge unnecessary cost on public infrastructure. There is no reason that grey rainwater would not serve more efficiently, gifting car owners and their supply chains a measurable "green" giveback by not requiring the transport and supply of heavy liquids.

The repair bill after you forget to add the anti-freeze would more than make up for any convenience gained. If you can't remember to fill the fluid tank what makes anyone think you would remember to add anti'freeze when the seasons change?

I have the car regular serviced, when the lights go on; i've taken it in for all its honda-services. They fill up the oil and the antifreeze already; (the only time i ran out of wiper fluid in the past years was during a light rainstorm driving from Glasgow to Edinburgh, windscreen covered with filth, using a tissue out the window to keep it visible - and that after it had rained all the night previous - when it could have been topped up the fluid.) A lot of the world is temperate, especially where it rains much, and the need for antifreeze is less a matter in such climates.

sweetheart:

That's good. Just don't forget the float diverter so you don't overfill the holding tank and wash out the windshield solvent.

The same system could feed the radiator overflow tank.

What makes you think the water saved would offset the water required for the construction of the rainwater diverter?

You would need the diverter to dump excess rainwater when the washer reservoir gets full, so it (and the fluid concentrate) don't get dumped onto the street.

Around here (Canada), you buy pink fluid in the summer, which is formulated to clean bugs and dirt from the windshield. You use blue fluid in the winter, which is largely alcohol to combat ice.

If the bottom of the windscreen is used as the rain gutter, given that my current windscreen reservoir is directly beneath this connected to the firewall, the additional plastic needed to have a small supply, filter float valve and overflow drip tube would be a bit more plastic - possibly no more plastic than a single large container of undiluted washer fluid. Arguably, depending on design, no more materials would be used than are already used, just a slightly different layoutof the refill tubes - with the screenwash concentrate held entirely separate from the water mixture reservoir.

Rain water as well tap water will freeze inside the tank, small pump, hoses, etcand destroy it. You must use windshield wiper fluid which will not freeze.

Sweetheart, forgive me for not getting this but you said, "the only time i ran out of wiper fluid in the past years was during a light rainstorm driving from Glasgow to Edinburgh, windscreen covered with filth, using a tissue out the window to keep it visible - and that after it had rained all the night previous".

And the rain wasn't enough to clean the windshield. So you want to save rainwater to use to clean the windshield? Don't you have windshield wipers?

Yes pilsner;The rain in scotland can be very very light, not enough to washthe road or the windows, but enough to kick up immense tyre-grime making a wash and wipe necessary every 30 seconds in the worst conditions. In exactly these conditions, the visibility can be zero without wiper fluid - all the wipers do without fluid is smear the mudlike grime in to a brown rainbow.