There is an advertising illustration of a woman wearing a silk slip and washing her hair in a pool of water by John La Gatta (1894-1977) coming up for sale on June 5, 2018 at Swann Auction Galleries.
See this link to the National Museum of American Illustration for more information about the artist,
The illustration in the sale might have been done for Laros Lingerie c. 1940 for either a magazine ad or Laros catalog.
Below is an similar illustration by La Gatta for Laros:
In 1938, Laros come out with “Dimensional Slip” which was billed as the best fitting slip on the market:
This image comes from a history of the company: