The Construction (Design and Management) Regulations set out the minimum requirements for welfare on a construction site.   If you have overall control of the site, you are responsible for making sure that legal requirements for welfare are met for the site. In practice, this means the principal contractor or other person in control of the site will often either provide or arrange for common facilities for everyone.  If you are an employer or are self-employed, you need to ensure that everyone working under your control is either provided with or has access to suitable welfare facilities.