A few thoughts about windscreen washers:

Not many people realise that it is illegal to be driving a car without washer fluid in the reservoir. However, apart from staying legal, you really don't want yourself suddenly needing to be able to clear your screen and finding that your windscreen washer is empty.

Ideally motorists should top up their windscreen washers reservoir when doing their weekly checks but in reality few will actually bother to do this. Apart from topping up there is no easy way to check how much fluid is left as most cars do not have a warning light to let you know that the level is getting low. Although there is a maximum level marker on all the cars I know of there is no visible minimum level marker. Many motorists do not top up until the reservoir is already empty. This can cause problems with sediments from the bottom of the reservoir entering the pump or the spray feeder tubes or the nozzles and creating blockages.

Many motorists do not know what the capacity of their windscreen washer reservoir. How can they know when this information is not even in the handbook? The main internet search engines show evidence of motorists trying to find the capacity for their cars and generally only filling when empty. Car manufacturers use bespoke reservoirs which are carefully designed to fit into whatever available space has been left over. Capacity would seem to vary between 2.5 and over 5 litres, and is greater if the vehicle has headlight washers as well. Ready-to-use screen fluid is sold in 1 litre, 2.5 litre and 5 litre containers, but of course with concentrated fluid motorist can mix up whatever quantity they need.

So although the best advice is definitely to top up weekly many motorists would probably not do this and like me would probably prefer some sort of dashboard warning that the reservoir was low or needed to be topped up. This is not something that it would be easy to retro-fit because of the awkward location of the reservoir and the need to introduce a warning light circuit into the wiring loom, but it would not be that difficult during the manufacturing process. It would be interesting to know what it would cost for manufacturers fit low level warnings for the windscreen washer reservoirs and if motorists would be prepared to pay for this.