Answer:
If by 1:3 ratio, you mean that you have 4 total parts. Then 1.5 litres of water is used with 0.5 litres of squash to make 2 litres of drink.
Explanation:
1+3 = 4 parts of drink.
2L / 4 = 0.5 L
1 part squash = 0.5 L squash
3 parts water = 1.5 L water