lossing weigh

ok so im 280lbs and i want to Water Fast to lose weight. i have a few questions please answer soon i want to Water Fast which i can only thing is, is that i work and at work we are all close and eat lunch together they wont understand and think im starving myself what should i do
second question is this the best way to lose weight or should i just diet
third question will i lose more if i lightly workout