I'm going to assume IWW is First World War :).

Where they moved to Palestinian grounds?

Well, throughout the actual war when the land was separated (during the Civil War from 1947-1948, and the Arab-Israeli war from 1948-1949), there were around 710,000 Arabs who were forced out or fled due to a multitude of reasons into neighboring areas. Around 350,000 ended up in Jordan (Jordan including the occupied West Bank, where most refugees were), 200,000 in the Gaza Strip (occupied by Egypt), 100,000 in Lebanon, and 60,000 in Syria. Half settled into existing towns and villages, and half settled in camps.

Now, after the war ended Israel offered to take back around 65,000-70,000 refugees, if the rest of the countries around would assimilate them and "settle the account" so to speak. The offer was refused, most Arab countries choosing the "all or nothing" approach.

Arabs living in Israel after the war were kept under martial law, until around 1966. Despite being classed as citizens of Israel, these were the same groups the Israelis felt posed the biggest threat: a threat from within. As such, they were viewed as subversives. Most lived along the armistice lines, designated military zones, and thus were not subject to civil laws, but rather military edicts. The frequent incursions of Palestinians into Israel (many border clashes especially in the 1950s and 1960s would occur) spooked Israeli leaders, who felt that empowering Palestinian Arabs with full rights would cause a "fifth column", and the military kept the freedom to confiscate entire villages of property if they felt the need. Tens of thousands of Arabs had their lands confiscated under an absentee land law that said that if they had left their homes after the UN Partition Plan passed, they were classed as absentee, and had to prove they were not. Some received compensation if their lands were taken under this law, and some were allowed to lease back their land, but the use of deserted housing to house the new Jewish refugees (the population of Israel doubled within 4 years of its establishment, over 650,000 Jews arrived from 1949-1952) became a crucial way of solving the housing shortage.

Before the First World War, the best estimates we have are difficult to verify. Sergio Della Pergola estimates 94,000 Jews in 1914, Justin McCarthy suggests 59,000. The truth is, census-taking at the time was poor and the population was in flux, so the 1914 Ottoman census is not really reliable in most cases.