clickdetector clicked if Used = True then "Red Line"? [SOLVED]

that because you put end before elseif

move end to line 31

your second problem is you put elseif on line 17 but you put then on line 18

Your script will be like this

local TweenService = game:GetService("TweenService")
local Water = script.Parent.Parent.Parent.Water
local Using = false
local Goal = {}
Goal.Size = Vector3.new(1.78, 0.50, 2.48)
local Goal2 = {}
Goal2.Size = Vector3.new(1.78, 0.05, 2.48)
local TwInfo = TweenInfo.new(5)
local TwInfo2 = TweenInfo.new(15)
local Tween = TweenService:Create(Water, TwInfo, Goal)
local Tween2 = TweenService:Create(Water, TwInfo2, Goal2)

script.Parent.ClickDetector.MouseClick:Connect(function()
    if script.Parent.Parent.Parent.IsUsing.Value == true then
        print("yes")    
    elseif script.Parent.Parent.Parent.IsUsing.Value == false then
        script.Parent["Waterfall Sound Effect"]:Play()
     if script.Parent.Parent.Parent.Sink.WaterGo.WaterFall.Enabled == false then
        script.Parent.Parent.Parent.Sink.WaterGo.WaterFall.Enabled = true
        script.Parent.Parent.Parent.Water.Transparency = 0 
        script.Parent.Parent.Parent.Water.Texture.Transparency = 0.8
        Tween:Play()
        wait(5)
        script.Parent.Parent.Parent.Sink.WaterGo.WaterFall.Enabled = false
        script.Parent["Waterfall Sound Effect"]:Stop()
        Tween2:Play()
        wait(15)
        script.Parent.Parent.Parent.Water.Transparency = 1
        script.Parent.Parent.Parent.Water.Texture.Transparency = 1
     end
    end
end)