There are two types of water purification and storage strategies:
Short Term (3 to 12 months), and
Long Term (1 to 5 years).
Chlorine is cheap and commonly available and is often used to treat water for bacteria.
Clorox/Chorine (CL01 liquid) can purify ("kill bacteria") in water for 3 to 6 months of storage. Unfortunately, liquid CL01 itself expires after about 1 year and become ineffective.
CONS: CL01 can be much more dangerous to mix if you get things wrong. Chlorine (CL01) build-up can become toxic over time depending on how your mix it.
Calcium Hypo-Chloride Powder aka "Pool Shock" - breaks down to Chlorine (CL01) when added to water.
Cannot be used for long-term water storage. Can be stored in powder form for 10 years. After use, still only purifies water for 3 to 6 months.
Make sure to get one that is minimum 65% Calcium Hypo-Chloride.
PROS: Cheaply available, used in the Pool Industry, many preppers tend to recommend Calcium Hypo-chloride is because it is the preferred long-term storage form of Chlorine (CL01) since it has a shelf stable life (in dry powder form) of 10 years, while Chlorine and Bottled Clorox in liquid form only last maybe a year.
CONS: CL01 and Calcium Hypo-chloride can be much more dangerous to mix if you get things wrong. Chlorine (CL01) build-up can become toxic over time depending on how your mix it.
DANGERS: These chemicals are much more dangerous to store, are much more corrosive (can eat through metal shelves), and flammable upon interactions with other things. These chemicals are similar to the Chlorine Gas weapons used in World War 1. So, if you are educated in its controlled storage, mixing, and use then you are safe. If not, you can kill yourself and others.
Chlorine Dioxide (CL02) for long-term water storage of up to 5 years. a completely different chemical than CL01 (Chlorine)
PROS: Doesn't have the chlorine taste, is anti-viral, anti-bacterial, and prevents slime build-up. Bacteria can grow in slime, so CL01 is not a complete solution against it. If you use city or municipal water, you've probably already been drinking CL02 in your tap water.
See AquaMira Chlorine Dioxide. This product is sometimes included in bulk water storage kits.
CL02 is the only 'complete' long-term solution against bacteria, slime build up, and odor.
OTHER USES: Also sold as a superior anti-bacterial and anti-virtual cleaner for use in clinical, hospital, restaurants, and the home kitchen. It was used to combat the spread of COVID. It is also used to properly kill molds and mildew without causing spores to spread - unlike with chlorine (CL01).