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.
Chlorine gas is primarily used as a disinfectant for treating water supplies around the world. The main applications are treatment of drinking water and industrial and municipal wastewater treatment before discharge. Other usages include disinfectant and algaecide in food processing systems, and water cooling systems.