Rainwater Harvesting and other plumbing considerations

For awhile, I've been interested in the idea of harvesting rainwater from the roof to use for potable and non-potable water needs in the house.  I first heard of it in Bellingham, WA, at a water conservation expo, and the idea has fascinated me ever since.

Here in Montgomery County, MD, they are pretty big on stormwater management (SWM).  The soil on our lot (indeed, in most of Poolesville) does not infiltrate very well, if at all, so most SWM concepts are out the window.  However, rainwater harvesting is one of the options the County allows for meeting SWM requirements.

My current plan is to use six 1,700 gallon tanks buried in the ground near the house to collect the rainwater.  They look like the picture below.  The green thing on top is a childproof manway.

We have town water available, but the quality, frankly, isn't all that great (it's extremely hard) and water main breaks are a frequent occurrence.  I would still connect the town water to our system, downstream of purification devices.  I drew up a schematic, below.  Hopefully you can click this link here to see it full size.

Aside from the tanks and getting the rainwater to the tanks, it's not much different than having a well.  We'll see if the County goes for the non-potable users...a read of WSSC standards indicates only toilet flushing would be eligible for that; lawn sprinklers and outside hose bibs have to be potable, which is ridiculous in my view.  If that's the case, then we'll just make it all potable and simplify it.

I'm also going to put in hot water recirculation.  There will be 3 main trunk lines for hot water serving the 3 main areas that have bathrooms and the kitchen.  Each trunk line will be part of a loop that comes back to the water heater where there will be a pump.  Each loop will have a motorized valve on the return leg.  I'll put motion sensors in each bathroom and in the kitchen, so any time it detects motion and the temperature in the loop is below X degrees F, the valve on that loop's return leg opens and the pump kicks on for a short time period (like 20 seconds or so).  If I size the pump and trunk lines correctly, it should only take 7 - 10 seconds for the cooled water in the trunk line to get flushed with hot water.