Your definition of “interesting” may be different to mine, but this explains why it seems like the fountains are regularly “broken”. As the person responsible for the fountains within the overall Tooting Common Heritage project recently explained to us:

“…the push buttons have to be pressed 2 or more times to allow the water to flow through the water jets. This is due to the internal workings of the fountain that formed part of the lottery funding for the heritage project, whereby all of the internal workings of the fountain had to be engineered precisely to the fountain’s 1930s specification. Consequently the  system replicates engineering from yesteryear and is not in keeping with more modern water fountains.”

The upshot is “some patience will have to be exercised when using the fountain”.

Enjoy refreshing yourself in 30s style (although maybe wait until after everyone’s had their vaccines).