Water Meter

My city of Port Orange has electronic water metering that can be accessed by the water customer through Aquahawk. You can look at your water use down to each hour if you wish and the monitoring is accurate to 10 gallon increments. Potable water and reclaimed water have two different meters so they can be monitored separately. Your town/city may have a similar system and if so you may be able to use it to monitor your fill and accuracy would likely be better than a simple consumer item. If you area has such an option you'll need to create an on-line account with your information.

I used these when i filled my pool. Amazon.com: 2 Pack - P3 P0550 Water Meter | Measure Watering Use in Gallons or Liters |Fits Standard Garden Hose: Home Improvement

Cayman
This is just what I use to indicate my pool water consumption. The digital display indicates current flow to the pool autofill leveler and the total use. I reset the total at the beginning of each month. Eventually I will have a monthly and yearly indication of water use due to backwashes and evaporation.

Water Meter Solution

Several months ago, while I was in the middle of a Swimming Pool Equipment Pad renovation and rebuild, I became aware of just how much water my pool was losing on a daily basis (yes it was summer in the desert and I have a fairly large pool surface area). At first I thought I might have a...

www.troublefreepool.com

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So far, I am very happy now with this method of tracking my pool water consumption but I must say that it was a bit of a pain to install and did set me back about 5 bills total to include the metering device, digital display, plumbing etc, so this may or may not be a suitable solution for your needs and application.

This is just one of many solutions that may be available to you.
Good luck with your project.
Take care and the best.
r.