After wasting a lot of time on a related problem with LaTeXing a tilde, I thought I should record my results here in case it is a help to anyone else.
tldr: To avoid some of the difficulties of typesetting a proper tilde ~ character, I recommend adding
\usepackage[T1]{fontenc}
in the preamble of your latex file to get more modern versions of font encoding. On modern TeX installations, this automatically loads the T1-encoded version of Knuth's Computer Modern fonts.
Details:
As has been noted by previous posters, using standard pdflatex/latex with the default fonts (the original OT1-encoded Computer Modern), there are difficulties in trying to render a regular tilde character, ~, and there are various workarounds with varying degrees of satisfaction. One workaround is to use the textasciitilde command. For example, you can use it to put a tilde in a URL, like:
https://w3.pppl.gov/\textasciitilde{}hammett
This gives a raised tilde (the kind of tilde intended for accents over another character), and methods to lower it to a more normal tilde are discussed by other posters. While this works as expected if the resulting PDF file is viewed in Adobe Acrobat, a downside is that if the PDF is viewed with the built-in Preview app on a Mac (or if viewed in TeXShop's previewer, which uses the same Mac libraries for rendering), then this URL link visually looks correct as https://w3.pppl.gov/~hammett, but if you actually click on it, it gets interpreted only as
https://w3.pppl.gov/
If you try to cut and paste the whole URL from Preview into a browser, the tilde in the pdf is replaced with a blank
https://w3.pppl.gov/%20hammett
so it doesn't work. (If you paste into some browsers, there are other special characters added also). (The \url{...} command will display a URL with tildes correctly, but forces it to use a fixed-space terminal font, and there are times when you want to use a tilde somewhere besides in a URL.)
Investigating further, I learned that the character that latex puts into the pdf file is not a regular tilde character but a "Combining Tilde"
COMBINING TILDE Unicode: U+0303, UTF-8: CC 83
(previously known as a "non-spacing tilde", indicating its usage for accents over another character) and that is what Mac's Preview renders. This means that cut-and-paste from Mac's Preview into a browser fails.
However, Adobe Acrobat somehow implemented a workaround and when displaying the pdf converts this into a regular "Tilde"
TILDE Unicode: U+007E, UTF-8: 7E
so cut-and-paste of a URL with a tilde from an Adobe-displayed pdf file into a web browser works fine.
(I determined these unicode values by copying the rendered tilde character from the TeXShop Preview window and pasting it into the Character Viewer app in the menu bar on a Mac. Then right-click on the character to select "Copy Character Info". The Character Viewer app can be turned on in Mac Preferences, Keyboard, and select "Show keyboard and emoji viewers in menu bar".)
This problem goes away if you use T1-encoded fonts by adding
\usepackage[T1]{fontenc}
to your latex file preamble. Furthermore, if you use the Adobe Times-like font
\usepackage{newtxtext}
then tilde is rendered at mid height automatically and doesn't need to be lowered. (The above command uses the newtx font only for regular text, while leaving the math fonts unchanged. I like newtxtext because it is slightly darker than CM. But for math I prefer to keep Knuth's traditional Computer Modern CM font, because the newtxmath font, like other Times math fonts, renders math italic v in way that is confusingly like a Greek nu.)
P.S.: For more info on why it's always good to use the fontenc package for a more modern approach than the 1970's original encoding, see (1) https://www.texfaq.org/FAQ-why-inp-font, (2) https://tex.stackexchange.com/questions/664/why-should-i-use-usepackaget1fontenc, and (3) https://en.wikibooks.org/wiki/LaTeX/Fonts.