"I thought to myself, it really looks like a big canvas for a graffiti artist."
She said it would be "tempting" to some.
DaSilva took her husband up to the tank about 3.30pm the same day to see if he noticed the difference.
There are some in the community that take pride in defacing even the most beautiful art on public and council assets.
They walked around and discovered the tank had already been tagged.
"Being an artist myself, I always appreciate art and actually enjoy the ever-changing colourful works that come and go on the water tower," she said.
"Perhaps it should be made an official place for graffiti artists, since it is obvious that painting over it doesn't stop the taggers."
Council graffiti programme adviser Hine Sullivan said their contractors will be removing the new tags.
"International studies/research has shown that rapid removal is one of the best ways to deter this type of activity, as the main aim of the vandals is to gain notoriety," Sullivan said.
"Rapidly removing their unsightly tags doesn't support this concept and eventually the vandal desists.
"I do understand what Swan is referring to about the changing colourful work on these sites, and agree that it can be fantastic."
However, some of the graffiti could be "very offensive", she said.
"There are some in the community that take pride in defacing even the most beautiful art on public and council assets, with little regard to the cost property owners must meet to remove it and the effect offensive graffiti has on the public.
"In relation to the graffiti that has appeared on these water tanks, our contractors will remove the tags. This site is being considered for an upcoming art festival, which will include local and international artists."