How to stop windscreen wash fluid freezing?

[FLAT 6]

Any of you chemists out there know what I could add to the already concentrated windscreen wash I'm using to stop it freezing? I'm thinking meths or somesuch but don't want to use something that might damage paintwork.

Maybe it's just that Homebase's 'concentrated' is not as concentrated as others? Anyone else had this problem?

[FLAT 6]

Yep - frozen in the bottle. And in the plastic container in the garage.

I see recommendation for Methanol or Vodka on a web search.