washer fluid is no science, but common sense.
the Alcohol keeps the ice is gone, the ammonia water removes trafikfilm, the detergent takes the grease and emulgerer fat and water.
do you Use tap water, you should add a bit of lemon - or vinegar-acid. You can find kalkfrit water for a decent price, it is preferable.
Alcohol is clearly the most expensive ingredient, but costs 20 kr. pr. litres you end up with about 5 litres of washer fluid for a good 20 kr. The alcohol should preferably not be increased, because there is acetone in. Unfortunately, pure alcohol is in practice impossible to find in Denmark.
TIP: the water from your condensation-dryer is kalkfrit, use it to your homemade washer fluid.
Warning for the most thirsty: do not Drink alcohol, as you are going to pour in sprinklerbeholderen. It might give you a good breath, but tastes ad Pomerania.