Actor.cpp

void CActor::OnDrink(float fWater) {
	if (fWater > 0.0f) {
		float oldWater = GetWater();
		float newWater = oldWater + fWater;
		SetWater(newWater);
	}
}

BasicActor.lua

function BasicActor:OnDrink(fWater)
	self.actor:OnDrink(fWater);
end

ScriptBind_Actor.cpp

SCRIPT_REG_TEMPLFUNC(OnDrink, "fWater");
	
...
	
int CScriptBind_Actor::OnDrink(IFunctionHandler *pH, float fWater)
{
	CActor *pActor = GetActor(pH);
	if (!pActor) return pH->EndFunction();
	pActor->OnDrink(fWater);
	return pH->EndFunction();
}

Well.ent

<Entity
	Name="Well"
	Script="Scripts/Entities/Others/Well.lua"
/>

Well.lua

Script.ReloadScript( "Scripts/Entities/Actor/BasicActor.lua");

Well = {
	Properties = {
	  -- need a model...
		object_Model = "Objects/props/furniture/appliances/ceiling_fan/ceiling_fan.cgf",
		fWater = 20,
		bUsable = 1,
		sUseMessage = "Drink",
		Physics = {
			bRigidBody = 0,
			bRigidBodyActive = 0,
			bRigidBodyAfterDeath =1,
			bResting = 1,
			Density = -1,
			Mass = 150,
		},
	},
	Editor = {
		Icon = "animobject.bmp",
		IconOnTop = 1,
	}
}

MakeUsable(Well);

-- Default entity functions

function Well:OnInit()
	self:OnReset();
end

function Well:OnSpawn()
	self:OnReset();
end

function Well:OnReset()
	if (self.Properties.object_Model ~= "") then
		self:LoadObject(0, self.Properties.object_Model);
	end
	self:PhysicalizeThis();
end

function Well:PhysicalizeThis()
	EntityCommon.PhysicalizeRigid(self, 0, self.Properties.Physics, 1);
end

function Well:OnPropertyChange()
	self:OnReset();
end

-- Usable entity functions

function Well:IsUsable(userId)
	index = 1;
	return index;
end

function Well:GetUsableMessage(index)
	return self.Properties.sUseMessage;
end

function Well:OnUsed(userId, index)
	userId:OnDrink(tonumber(20));
end