On my laser I have a detector unit that beeps when on the centre of the beam. At 300 ft it is still accurate even though the beam has spread to an inch dot.Part of it was that laser line at the distance was not very sharp.
For a water level I have an electronic one that beeps when the water touches the mark on the fixed end similar to this.
Accurately find level with the Zircon WL25 electronic water level. Use to install decks, fences, chair rail, drop ceilings, and more.