No, there is no wheather instruments having lawn guages for how much to water
The first and foremost thing in keeping a lawn nice is water. If the lawn does not get enough water, it will dry out and turn brown. Keep the lawn trimmed, and make sure it gets plenty of water, especially if it is getting hit directly by the sun with no shade.
you can wash it on your lawn, that means your lawn will get watering
There are a couple advantages. You do not have to mow the lawn and you do not need to water it.
no
The salinity of sea water (Atlantic 3.1% or Pacific 3.3%) is great enough to seriously damage grass in a lawn.
There are several ways in which one could treat a neglected garden lawn. These including measuring the right amount of water to water a lawn, spot spray individual weeds, and vacuuming pebbles on the lawn.
Mow it weekly and water it.
no
in the afternoon
You do not have to manually water your lawn all of the time. Some people cannot do this if they are on vacation and can't water their lawn, or if they work a lot and simply do not have enough spare time. Also, it times exactly the time and the amount of water your lawn needs.
it sprays water over your lawn so it can grow more easily.
It will not hurt your lawn if you drain your pool water onto it. However, if you don't want a mud puddle, drain it on a down slope where the water will run off and not just sit on your lawn.