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At first sight, transparent water containers could be perceived as good options, because it can help the user to see the inner surface walls. The idea is: "when the walls look dirt, it is time to clean them".

However, the big drawback of a transparent container is the rapid growth of algae caused by the passage of sunlight. Instead of using transparent containers, it is recommended to use opaque containers and set up a schedule for cleaning. The safe water storage containers should be cleaned in a regular basis (it is highly recommended before every use) and the treated water consumed in 1-2 days of treating it. 

In some publications, it is stated that the maximum interval for cleaning the water containers is one week. 

Check the following resource for more details on how to handle the water container. 

This question was raised during the webinar "A water professional’s guide to safe storage". If you missed this webinar, please find it here. 

During the webinar on "A water professional’s guide to safe storage', due to time constraint, the speakers could not answer or discuss with all the participants the questions raised. 

If you missed this webinar, please find it here. 

Here another great question raised in the webinar: 

Is there any country who has developed regulation for water storage container? (Countries where containers/jars are widely used for water transport?)

@Brian Reed made a great observation during the webinar about a student project (unpublished) on removing algae from plastic containers. 

From the existing literature, when conducted properly, the method of cleaning plastic containers using sand seems to be effective, but it may lead to premature aging of the container.

Check the following resources and studies for more details on this topic.

1.  Selecting a Drinking Water Container for Household UseCAWST (2021)
2.  Keeping water from kiosks clean: Strategies for reducing recontamination during transport and storage in Eastern Uganda Gärtner et al. (2021)
3. Efficacy of locally-available cleaning methods and household chlorination at inhibiting biofilm development in jerricans used to store household drinking water  String et al. (2020). Download the author version here.