By Francesco Amicone
Dave Smith, Los Angeles Times journalist, wrote in 1969:
“Dr Leonti Thompson, a psychiatrist at Napa State Hospital 15 miles north of Vallejo, has found a number of different meanings in the killer’s crossed-circle “signature.” In one primitive culture it represents the earth; in another, the ancient notion of the four elements that make up the world: earth, air, fire and water. Still, another symbol, the “X”, represented water in the alphabet of the legendary continent of “Mu”. ‘And the killings took place near water,’ Thompson notes speculatively.”
“Zodiac Killer, chilling portrait of madness“, Los Angeles Times, October 15, 1969, p. 126
Robert Graysmith revived this theory in 1986:
“I thought it was strange that the killings so far had taken place in locations that had a form of water in their name: Lake Herman Road, Blue Rock Springs, Lake Berryessa, and Washington Street, which was quite close to Lake Street.” Robert Graysmith,
“Zodiac“, p. 146
It is observable that all the places of Zodiac’s official assaults and locations of phone booths where he called the police had a reference to the “water” and “wash”. Zodiac mentioned the water in one way or in another one in several letters, too. I put these references in the following list.
List of references to water by Zodiac
1. Riverside, October 30, 1966 (the city where the murder was committed);
2. Dive watch Zodiac Sea Wolf, 1967 (advertisement);
3. Lake Herman Road, Vallejo, December 20, 1968 (crime location);
4. Blue Rock Springs, Vallejo, July 4, 1969 (crime location);
5. Springs Road and Tuolumne Street (oil and gas station Joe’s Union), Vallejo, July 5, 1969 (phone booth location);
6. «Water hose», August 4, 1969 (letter);
7. Lake Berryessa, September 27, 1969 (crime location);
8. «I am drownding (sic)», December 20, 1969 (letter);
9. «Blue meannies (sic)», “Yellow Submarine” (movie on The Beatles), April 20, 1970 (letter);
10. «I was swamped out by the rain», April 20, 1970 (letter);
11. «I shall listen to their pleass for water (sic)», July 26, 1970 (letter);
12. «I am crack (instead of water) proof», October 5, 1970 (postcard);
13. «By fire, by gun, by knife, by rope (on the cover he copied there was also “by water” which here is omitted)», October 27, 1970, Halloween card (based on the cover of Tim Holt No. 30, discovery by Tahoe27 here);
14. «I am crack (instead of water) proof», March 13, 1971 (letter);
15. «Blue meannies (sic)», “Yellow Submarine“, March 13, 1971 (letter);
16. «He plunged himself into the billowy wave and an echo arose from the suicides grave» (a “death by water”, excerpt from “The Mikado” by William S. Gilbert and Arthur S. Sullivan), January 29, 1974 (last signature).
Monster
It has been recently discovered (here’s the news) that also the Monster of Florence did the same in his only official letter postmarked September 9, 1985.
17. The title of the main article the Monster cut for his message contains the only whole word (“Della”) the mass murder pasted on the envelope. It reads: «Dear sweet waters, I do not know you anymore: my childhood dream is ended here». From here, the murderer cut other two letters: the E of acque, waters, and Z. 
List of references to “wash” by Zodiac
1. Washing line (link), September 27, 1969 (evidence);
2. Car wash (link), September 27, 1969 (phone booth location);
3. Washington Street, October 11, 1969 (crime scene);
4. «Washington street», October 13, 1969 (letter);
5. «I just washed my pen», November 8, 1969 (greetings card).
Monster
6. The “Italian” serial killer cut the punctuation from an advertisement for a washing machine brand as below.
