For collecting rainwater for irrigation and processing greywater make a pond, stock it with plants, fish, frogs
with edge plants as dragonfly habitat, and put up some carnivorous bird houses, here's a good one for multiple species
http://www.50birds.com/MPSideMount.htm
If you need to get drinking water out of it, then use a reverse osmosis system with sediment filter.
Even if you have roof collected rain-water for drinking still have to filter out bird-poop and such.
If you have a lot of night-insects you'd like to get rid of, get bats.
a single bat eats 1000+ mosquitoes/moths per night,
typically a single bat house holds hundreds of bats.
Also unlike dragonflies, bats are active at night,
same time as mosquitoes are.