You cannot cheat the game and use tools for no reason in Innocent Life Futuristic Harvest Moon; however, you exploit the system and use tools after certain tasks or activities are done.
For the watering can just till a square of soil and you can water that square once with the can. Note that the item ''strange moss'' prevents you from watering the affected square daily, so use this exploit on squares that are virgin.
As for the hammer and hoe, there is an exploit to use them on a single square so long as your character has PP to spare. Use the hoe to till a square then use the hammer to ''untill'' the square. Go back to using the hoe and repeat. All this can be repeated so long as you want to expend PP.