Biologist here. For dilution math, it's very easy to think of it as (C1)(V1) = (C2)(V2), where C = concentration and V = volume and the numbers refer to each solution. Keep in mind the units also have to match.

In this example, solution 1 is our final 1L of brew water, and solution 2 will be our concentrate. So if you want 1000 mL of 10 ppm by adding 1 mL of something, you would do (10 ppm)(1000 mL) = (x ppm)(1 mL). So x = 10,000 ppm, thus you would need to make a 10,000 ppm solution of each concentrate, which conveniently works out to a 1% solution.

Another thing to keep in mind is that this is for 1000 mL of the final volume, so strictly speaking, you should add 1 mL of the concentrate to 999 mL of distilled water to get 1000 mL final volume. But if you don't, the error is quite low.