Weight of Imperial Gallon of Water.
1 gallon [UK] = 1.201 gallon [US, liquid]
One US gallon weighs 8.34 pounds, so an imperial gallon weighs about 20 percent more, or almost exactly 10 pounds.
Weight of a Gallon of Salt Water.
See the web links below this answer for an automatic calculator that will give you the density of water at whatever temperature and salinity you want. Once you know...
Liter is another unit of volume, not really useful to express weights.One US gallon is 3.875 liter, which in water will be real close to 3.875 kilogram, or kilo for short, which is an unit of weight.