Hi,
I'm going to assume that the pipe coming out of your house has already run through the meter (just a guess).
If the water for the irrigation is supplied by the local municipality and is plumbed accordingly from up side of the main meter there *could* be two water meters, the house main meter and an irrigation meter. The reason that the irrigation is metered separately from the main house supply meter is so that you do not pay for sewer charges for the irrigation water.
And yes there should be a backflow preventer to keep the irrigation water from backflowing to the main water supply.
Nick, if the space is indeed for a meter you probably need to contact the county or whomever supplies your water to request an irrigation meter, they will inspect to make sure all connections, backflow preventers are within code and correct.
If your water is supplied by a well (I doubt it, the lines are much too small) then disregard my assumption that the empty space is for a meter.
