On the set, Joanne Woodward told the then seventeen-year-old Melanie Griffith, who was playing her daughter, that she had three goals in life: Marry a movie star (Paul Newman), have beautiful babies (she had three), and win an Oscar (which she did in 1958). Melanie said that she adopted those goals for herself by marrying a movie star (Antonio Banderas), having beautiful babies (she also has three), but expressed frustration that she hasn't won an Oscar, even though she was nominated in 1989 for the Best Actress Academy Award for Working Girl (1988).
The Lew Harper character was originally known as Lew Archer in the series of detective novels. According to Frank Miller at the TCMDb, for the first Paul Newman Lew Harper movie Harper (1966), the success of source novelist Ross Macdonald's Lew Archer detective series "didn't stop [actor Paul] Newman from changing the name of Macdonald's most famous detective, however. Struck by his success in two films beginning with the letter "h" - The Hustler (1961) (1961) and Hud (1963) (1963), Newman asked that the private eye's name be changed from Archer to Harper". However, alternatively, Wikipedia states "The name of the lead character was changed from Lew Archer to [Lew] Harper because the producers had not bought the rights to the series, just to 'The Moving Target'. [Screenwriter William] Goldman later wrote 'so we needed a different name and Harper seemed OK, the guy harps on things, it's essentially what he does for a living'."
According to the biography "Paul Newman: A Life" (2009) by Shawn Levy, Newman had an almost major accident whilst racing a Porsche car at a New Orleans race-track off set during production. According to the book, Newman and a cohort were not wearing seat belts when the vehicle spun out of control. Newman said: "For a time we rode on two wheels. Then the car went on its side but we weren't thrown out. The windshield shattered. Fortunately it was European glass that breaks into powder on impact. We climbed out of the windshield. Neither of us was hurt. We hardly had our hair mussed. As I stood by the car, somebody slammed the door on my hand. Fortunately the door was sprung or I would have lost the tips of my fingers. 'Open the door' I said quietly. When they did, I ran to the beer cooler and stuck my fingers in the icy water. I didn't even lose my fingernails." Incidentally, in the earlier Lew Harper movie Harper (1966) starring Newman, the make and model of Lew Harper (Paul Newman)'s car was also a Porsche, a black-top gray / silver Porsche 356 A Speedster.
The studio sound-stage that was used to house "the Drowning Pool" was Stage 15 at the Warner Brothers Burbank Studios. The stage had been a studio watering place for such earlier pictures as the marlin fishing scenes in The Old Man and the Sea (1958) and the Arctic ice floe sequence in The Great Race (1965).
Actor Paul Newman once said of the Lew Harper character in the "Paul Newman: A Life" (2009) biography by Shawn Levy: "I simply adore that character because it will accommodate any kind of actor's invention...It's just lovely to get up in the morning, it's great to go to work, because you know you're going to have a lot of fun that day".
During post-production, director Stuart Rosenberg hired Composer Charles Fox to do additional scoring, integrating the composer's melody "Killing Me Softly With His Song", into the movie. The song had been a #1 hit two yrs prior, while Fox was scoring Rosenberg's previous film, "The Laughing Policeman"
Paul Newman: [H] The character Lew Harper is based on novelist Ross Macdonald's character Lew Archer. The name was changed for the first 'Lew Harper' film Harper (1966) supposedly because Paul Newman had recently enjoyed success with Hud (1963) and The Hustler (1961) (two of his successful films beginning with the letter "H", a later one after Harper (1966) was 1967's Hombre (1967)) and the producers wanted the movie's title to begin with "H". Also, the Macdonald estate did not want the name "Archer" used in the movie. There may have been fear of legal complications because Macdonald got the name "Archer" in the first place from Miles Archer, Sam Spade's partner who is killed early on in Dashiell Hammett's The Maltese Falcon (1941)".