Regular Expression Vaidator - How to add spaces to the following Validator

I have the following validator string - ValidationExpression="^[A-Za-z0-9~!@#$%^&*()_+`\-={}\[\]:;'<>,./?']{1,20}$"

The validator is suppose to allow any keyboard key to be typed into the textbox. However, one that was missed was the space bar. Right now if you put a space between the two words it generates an error.

Question: How would I add "space" as an allowable key.

...