My water is stored in a dark and cool food cellar that stays at 12-15°C (Below 60°F) all year round and in sanitized food-safe water containers. So far the water has had neither colouration, smell or taste after a year of storage.

The next bit is a citation from “Livsmedelsverket”, which is responsible for food safety in Sweden, and has been through a rough Google Translate because it’s too long for me to care to manually translate it. A link to the Swedish PM is found at the bottom.

TL;DR: In a biologically stable system (low carbon content in the water and limited possibility of utilization carbon from the material, there is really no upper limit to how long the water can last stored from a microbiological point of view. This according to microbiologists and risk assessors at the Swedish “Enheten för biologiska faror” (Unit for biological hazards).

Preface
This PM constitutes a scientific basis for microbiological risks during the growth of bacteria in water stored in a can for a long time.
The material has been produced to order by The unit for sustainable food consumption and will be the basis for advice on how how long a consumer can store water.

Responsible for the report’s content is Jakob Ottoson, microbiologist and risk assessor at the Unit for biological hazards.
The report has been fact-checked by Roland Lindqvist, senior microbiologist and risk assessor at the Unit for Biological Hazards.

The Swedish Food Agency

[…]

Risk characterization
Questions and answers
The US Centers for Disease Control (CDC) has a website on behavior and storage of drinking water in cans Creating and Storing an Emergency Water Supply
| water, Sanitation, & Hygiene-related Emergencies & and Outbreaks | Healthy Water | CDC. Make Water Safe During an Emergency (Print-only) (cdc.gov)
Among other things, it is stated that the water is replaced every six months and that the cans are sanitized with chlorine.
a. Evaluate whether the information on the CDC website is useful for Swedish conditions.

Answer: The short answer is yes, the information can be used under Swedish conditions.
However there is theoretically no upper limit to how long the water can be stored.
For example, specified a shelf life of 2 years in tetrapack and 12 months in bag in box on the water that was taken revealed in a pilot study (Livsmedelsverket 2024b).
The specified chlorine concentration for sanitization is large and not really necessary (see further below).
Of the potential pathogens frequently detected in drinking water systems (see Hazard Identification), including bottled water,
M. avium and A. hydrophila have the potential to infect humans via the gastrointestinal system.
However, there is no epidemiological connection that this has happened and the likelihood of illness following consumption of stored water is assessed as very low and limited to an immunocompromised population.
However, smell and taste can be affected by any microbiological growth.
In a biologically stable system (low carbon content in the water and limited possibility of utilization carbon from the material, there is really no upper limit to how long the water can last stored from a microbiological point of view.

[…]

What is the best way to clean the cans?

Answer: The best way is to rinse out of the can.
Any remaining stains that may be made up of biofilm is wiped or washed away in a way that prevents as much as possible that the material is scratched because this gives bacteria in the water a larger surface to attach to and new carbon sources may leak from the material.
If necessary, cleaning agents, e.g. hand washing detergent, used, but then it needs to be rinsed off thoroughly.
If necessary, the can can be disinfected with chlorine.
However, the latter is not necessary as there are no obvious ones microbiological hazards in the water if it is initially of drinking water quality that was filled into a pure dunk (see answer to question 1).
A certain excess of free chlorine can, however, extend the time to the build-up of new biofilm (Huang et al. 2020) but can also lead to unpleasant odors and taste of the water and the formation of harmful by-products such as trihalomethanes (Food Administration 2024a).
In case of recurring problems with visible growth, smell or taste within six months, however, sanitizing with chlorine, or buying a new storage container, can be one alternative.
A spice measure (one ml) of chlorine (12% chlorine by weight) in three liters of water gives a total content chlorine corresponding to 50 ppm.
The vessel should be rinsed out after the treatment (in about 30 minutes) and air dry before refilling with new water.

Citation from
Livsmedelsverket. Ottoson, J. 2024. PM 2024: Vatten på dunk - Riskvärdering. Livsmedelsverkets PM. Uppsala.
PM 2024
ISSN 1104-7089
https://www.livsmedelsverket.se/globalassets/publikationsdatabas/pm/2024/pm-2024-vatten-pa-dunk-riskvardering.pdf