You can go online at Costco.com and apply for a Costco Membership there by adding it to your shopping cart if you are shopping for the first time. Your membership card will be mailed to you within 7-10 days but you can actually shop at the online store immediately.
The three most common chlorine-containing substances used in water treatment are chlorine gas, sodium hypochlorite, and calcium hypochlorite.
Since then, elemental chlorine dissolved in chemically basic water (sodium and calcium hypochlorite) has served a continuous function in topical antisepsis such as wound irrigation as well as with public sanitation i.e. swimming and drinking water.