any suggestions? Also what takes the freezing point down lower, say -10C?

Tell me if you find out I'm spending a fortune on the stuff!

Vodka.

Just use a solvent such as isopropanol (isopropyl alcohol) that'll mix with the water quite well, and add a bit of screenwash concentrate for cleaning power. That's what I used to do when I worked in a lab. Worked a treat. Then again, we did used to have big Winchesters full of IPA at the time.

deadlydarcy – how does the isopropyl go with the windscreen seals?

As far as I know, ok, never gave me any problems AFAIR…wouldn't swear on it though…maybe google…

The proper stuff is a mix of isopropyl alcohol and methanol . . . Buy it by the gallon from your motor factor for about 5 quid a gallon . . . -20C neat, -15C 1:1 with water -10C 1:2 with water . . .

Neat halfords concentrate seems to work down to about -12C ish before it slushes . . .

Fd

Dont buy that Pre mixed crap from Halfords at almost £6.00 gallon get a gallon of Holts concentrate for £4.00

Methanol and Ethanol is where it's at… just be careful – have the same type HSE restrictions as petrol.
IPA slushes up too early but is as some of the commercially available washes so not overly detrimental to anything else.

Vodka is cheaper than screenwash in Russia and is, therefore, a viable alternative. That does perish the rubbery bits in the system though.

vinegar

LIDL….

5 Litres
Effective at outside temperatures as low as -60°C
With practical, easy pouring spout
£ 3.99