This is a very difficult question to answer, as visa requirements differ between countries.
In general, house sitting could be classified as a job if you are charging for your house sitting services and therefore earning an income. If however you don't charge for house sitting, then a tourist visa should suffice (as house sitting is a free exchange of services) for most countries.
A few countries, however may take a harder line (eg. United States) and may consider all types of house sitting (ie. no charges) to be defined as a job, requiring a working VISA.
Regarding specific countries, the best advice that we can give is to visit the country's immigration department website and make an online enquiry.