Check my math please - RO reject reclaim

[Indiana Wash]

OK, I have my RO reject reclaim system working. I will use 100% of my reject water except on days when business ends suddenly and my RO tank is empty. Here is the way I look at it:

I have two LW4000's. I am guessing that I use 8-9 gallons per car. I have no idea whether I actually use that much but am just guessing. If anyone knows, please correct me.

I am also guessing that my reclaim is rejecting 2.5 gallons of water per gallon of spot free produced since most reject between 2 and 3 gallons per gallon of spot free.

I am just figuring for 10000 cars washed.

8 gallons per car times 2.5 of reject = 20 gallons wasted per car

20 gallons wasted times 10000 cars washed = 200000 gallons wasted

200000 gallons wasted / 100 gallons (price rate) = 2000 units of water

2000 units of water times $0.75 (my water and sewer rate) = $1500

So I save $1500 per 10000 cars washed. Does that look right to you?

 

[MEP001]

Looks right to me.

You could add an interlock on the RO system to shut it off if your reject capture tank is full.

 

[I.B. Washincars]

You forgot that you'll also save a bag of salt every now and then as well.

 

[Indiana Wash]

Looks right to me.

You could add an interlock on the RO system to shut it off if your reject capture tank is full.

I could, but instead, I added an overflow pipe to the capture tank and plumbed it to the drain. The capture tank fills pretty quickly. At times when the RO tank is empty, I still need to produce RO even though my capture tank may be full.

The good news is that with 2 x 2" BOB valves, I use up the reject water very quickly so it doesn't take many cars to use it all. As long as business doesn't end completely, I will continue to use all the reject.