Just to put things in perspective here your talking about around 5-10 pounds of salt depending on the size of the tub and how much salt there already is in your fill water. (The EPA allows up to 500 ppm TDS in drinking water, which typically would primarily be salt, and considers over 1,000 unfit for human consumption, a quick google search revealed municipal water reports showing slightly over 500 ppm salt to be somewhat common)