The weight of water can be obtained as a product of water volume and density. However, such calculations are not straightforward as the water density significantly depends upon temperature in a non-linear manner. It requires using tabulated density values versus temperature.
Calculate temperature in Celsius since temperature in these units is usually given in water density tables. Temperature(C)=0.55556 x (Temperature(F)-32) In our example, temperature(C)= 0.55556 x (86-32)=30.00 Celsius.
Navigate to "Physical characteristics of water" table and find in the column "density" a value (in kg/m^3) corresponding to the temperature. Divide this density value by 1000 to obtain it in g/ml units. In our example, water density at 30 Celsius is 995.71 kg/m^3=0.99571 g/ml.
Multiply water volume and density to calculate water weight. In our example, water weight =240 ml x 0.99571 g/ml= 238.97 g.