For the purpose we will use solution dilution equation:
c1xV1=c2xV2
Where, c1 - concentration of stock solution; V1 - a volume of stock solution needed to make the new solution; c2 - final concentration of new solution; V2 - final volume of new solution.
c1 = 70%
c2 = 25%
V1 = ?
V2 = 1000 mL
When we plug values into the equation, we get following:
70 x V1 = 25 x 1000
V1 = 333.33 mL
V(H2O)=V2-V1= 1000-333.33=666.67 mL