If you use the washers a lot then chances are that any bacterium are flushed out regularly and so do not build up. If you put washing up liquid in that can disrupt some cellular activity.

Same here.

Washing up liquid has no business being near a car.
Screen wash is hardly expensive, and helps clear the crap off your screen far better than water alone does.

Alex I bet you dilute your screenwash with mineral water.

RO water actually!

What and risk the mineral deposit build up?

LOL, screenwash is far too expensive to use all year unless you never actually drive anywhere.

A squirt of supermarket antibacterial washing up liquid costs about 0.01p compared to about 90p for the recommended dose of screen wash. It's even worse if you buy it at service stations.

I never use just water, because it really doesn't work. You need something to cut through the oil and dead flies.

That's on the hills above my house that is

And it's full of mercury - FAIL.

Washing up liquid [LIFTED] up your car in many ways:

The surfactants in washing up liquid aren't designed to get your windscreen clean or degreased. Chances are they'll knacker your wipers prematurely or damage the seals prematurely.

So, washing up liquid we've got salt (rust's best mate), surfactants (wetting agent will help water get behind seals, get under poor paint finishes taking the salt with it), formaldehyde (perishes rubber), sodium lauryl sulphate (from animal fats that'll stink after long enough).

Given that you can buy a 5 litre bottle of concentrate screen wash for about £3 near me, I don't think it'll break the budget of running the car, tbh.