Why don’t you try a water catch and use rain water?
How big of a water catch does one need to irrigate 1/2 acre during August?
For simplicity’s sake, let’s say that you wanted to double the amount of rainfall which the 1/2 acre gets. For that, you’d need a catchment area of 1/2 acre. You’d just add that water to the lawn in addition to the rain which fell on it. If you only needed to add half as much, your catchment could be 1/4 acre, etc. etc.
Do you have a general idea of how much water the lawn needs? I think Michigan gets, like, 3 inches of rain per month on average.
July and August are a little lean. Brown lawn where I don’t water. Green lawns on the two adjacent houses.
So a quick calculation (taking away the house footprint), I’d need to store almost 37,000 US gallons of water to approximate 3" of rain! I think I’ll verify my summer water bills and see how many “units” I actually consume those months, but if it is such a huge amount, it seems like it be simpler to use nature’s water tank rather than build something redundant.
Well, you wouldn’t need to store the entire amount if you are feeding it out all the time.
You might poke around the 'net and see if you can find out how much water you’d need for, say, a drip irrigation system. I’ve read that they use the least amount of water.
Example watering guideline here.