We have an oil boiler (new, self build house 2010) - house insulated to the nth degree, dual coil water tank to allow thermal solar panels to heat the water when it can - this has a big effect on bringing down our oil costs (1000l lasts 18months)
We collect rainwater - we have a 7000l tank in the ground behind the garage. We collect the water off the barn and garage roof. We use the water for loos and watering. If we were doing it again we would have 2 x 7000l tanks - mind you we were told that a 3500l would be fine for the 2 of us but we decided to double the size of the tank considering we were digging the hole in the first place. It's been great knowing that we aren't wasting expensively produced freshwater watering plants and flushing the toilet. Our water is supplied by South West Water - the MOST expensive provider in the country so we are very happy with our rainwater collecting.