Reducing Your Water Consumption

As I recently bought a house, I have been researching how to reduce the house's consumption of water and energy.

We have a 90 year old triplex in Philadelphia.

Our water consumption is currently 900 cf per month for 5 people. There are 7.5 gallons per cubic foot, so this is 6750 gallons or 45 gallons per person each day. According to the EPA the average American uses 100 gallons per day and 70% of that is for indoor purposes. Obviously outdoor watering (and pools) are huge users of water - by contrast my 100 sq foot veggie garden uses much less water and we don't water the lawn.

So our conservation is due to
-watering less outside (perhaps 1/10th of average US consumption)
-low-flow toilets. We replaced one 30 year old toilet with a 1.6 gallon per flush toilet. If you have old toilets, I strongly recommend getting 1.6 GPF (or maybe 1.2 GPF) low flow ones. They'll save you money and be good for the environment.
-not having a washing machine (this isn't really conservation - as the washing machine at the laundromat uses water on our behalf, unless by not having a machine we slightly discourage clothes washing)
-not having water leaks (dripping faucets, and more notably leaking toilets are very bad)

We've also setup two 55 gallon rain barrels that easily fill up if it rains. They sit on concrete blocks so they are high enough to provide pressure for a garden hose that waters the garden. Currently I'm experimenting with an easy system of dumping all the water over the course of an hour in one spot - providing 50 gallons of water for a tomato plant with deep roots (this is easier than setting up a drip hose). If we wanted to capture an inch of rain, we might need 12 rain barrels! While we do have an Elastomeric roof, my limited research is that while this does leach toxins into the water - it is hard to tell whether it is a major problem. I haven't seen any studies on this. I'm more concerned with the lead in the soil (up to 1000 ppm according to one test) that is below the raised beds and is slowing mixing in with the raised bed soil.

Future ideas for conserving water include
-more rain barrels
-a green roof - to reduce water getting into the sewer system and causing it to overflow
-either low-flow shower-heads or a recycling shower
-a gray water system (it should be fairly easy to dump the shower water in the backyard, though you need to be careful about killing things with soap. Or to use the rain water to flush toilets.)
-replacing hand-washing with a dish-washing machine (apparently hand-washing can be very bad, especially if you use hot water)
-replacing 2/3 of our front sidewalk with plants (it is 11 feet wide, but only needs to be 1/3 of that).
-replacing regular sidewalk/concrete with permeable materials

The Philadelphia Water Department has a map of storm water billing that includes an estimate of the area of impervious square footage in your property. They are currently transitioning the commercial and industrial customers to pay for their storm water impact based on the impervious area (as opposed to their net square footage). I think they have plans to do this in the future for residential customers as well, however they may face difficulties in actually measuring the impervious square footage for residential properties (as their map misses a lot). On the plus side, if they do implement this, they will provide a financial incentive for taking conservation measures.