About 96.5% (by weight) of sea water is water (H2O). The remaining 3.5% is about 3.2% sodium chloride (NaCl) and 0.3% magnesium sulfate (MgSO4). Also present are small quantities of calcium (Ca),...
No because the salt will kill the plants. Rainwater is very good for watering the garden because it contains no additives such a chlorine with is often present in tap water.