How do I figure the ratio of one part liquid to eighteen parts water if I am using four gallons of water?

Question

Isn't the water liquid also? So all eighteen parts are liquid.

17 parts water= 17/18*4gal= 17/18*16quarts= ...

1 part solute= 1/18*16 quarts= 3.5 cups

check my math

If you want a 1:18 ratio by volume, add 4/18 gallon of the other liquid to the 18 gallons of water. 4/18 gallon is 28.4 fluid ounces.

If you want a 1:18 ratio by mass, remember that one gallon of water weighs 8.34 lb (not 8 lb). So you would add (1/18)*4*8.34 = 1.85 lb of the other liquid