One of the basic components to sawmills is the drip tank, aka the lube tank. It provides water (or other mixture) that drips onto the blade while slicing through the wood. In essence, it lubricates and helps cool the blade; the lube makes it easier on the engine pulling the blade through the wood and the cooling helps keep the blade in better condition.
If you live in temperate climates like the southern US, you can probably get away with using water. For build up of pitch on the saw blade, you could add dish liquid or Pine-Sol to the water mix. But in climates where freezing can occur, you would be best to add windshield washer fluid to the water, or just run all windshield washer fluid. Some sawyers will even use diesel fuel as their choice of lubricant.
If you are going to use a windshield washer fluid, you should know that some of the store bought products have a wax additive. In cold weather the wax will congeal (clump) and as a result, will slow down and even block the line running from the tank to the saw blade. The only way to clean it up is to empty the tank, and flush it and the line with hot water. Lesson learned.