@Brian Reed made a great observation during the webinar about a student project (unpublished) on removing algae from plastic containers.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