Where the two wavefronts arrive in step, the water goes up further. Where they arrive half a wavelength out of step, they cancel and the water does not move at all. Those still lines are the nodes, and they are what makes the whole pattern measurable — because the distance between them depends only on the wavelength and the separation of the sources.
A ripple tank is a shallow tray of water with a lamp above it and two dippers that touch the surface. The crests and troughs of the wave focus the light into bright lines, so the pattern you see is a photograph of the antinodes. It was the standard demonstration of interference for most of a century, and it is still the clearest way to show that waves add.
What the tank gives you that a screen cannot is the fringe spacing: the distance between adjacent bright lines, measured on a straight line across the pattern. That distance is not arbitrary. It is set by the wavelength of the wave and the separation of the two sources, and the two together give the wavelength — which is exactly how Young's wavelength was first measured, and how it is still measured in a laboratory.
Put the two sources a distance d apart, look at a point a long way D away on the centre line, and the path difference is about d·x/D for a point a distance x from the centre. Constructive interference happens when that path difference is a whole wavelength, so the bright fringes sit at intervals of x = λD/d.
That single formula is why the fringes get closer together as you move the sources apart, and why the whole pattern narrows. Move the sliders and the fan of bright lines narrows exactly as the formula says it must.