The average depth of a residential swimming pool is between 3 and 4 feet deep and usually they are no deeper than 4 feet for safety reasons in a residential setting.
However you can have an 8 ft depth pool installed in your yard if you want too but the cost will be much higher than a swimming pool with less depth.
Most residential swimming pools I've swam in before have been 4 feet deep at most but I did swim in one residential swimming pool that was 8 feet deep.
But that was the only one I saw that was 8 feet deep but if your city or town allows the 8 feet deep pool and you can afford it then you can have one installed that deep.
If you have kids make sure you watch them and always have a fence around it to keep the kids from falling in and keep other kids out of it.