cisten pump sizing

Hello, I am looking for the following information. Can you help or at least point me in the right direction?
Sizing of pump and tank.
I am building a new home in a rural area that has a poor well supply (both volume and quality). Rural water may be installed in a year or 2 but for the time, I will be relying on 2 cisterns to meet our water needs. Our home is constructed on a hillside, and because of the grade, it was less expensive (compared to $7000 in fill stone) to construct a 10K gal and a 5K gal cistern (7’ deep) below the basement floor. The larger tank will be feed with rain/ roof runoff. Will install some type of filtration and water treatment system. the smaller tank will be used for hauled in drinking water (if needed). The basement height is 10’. While this is our retirement home, it has 3.5 baths as we have guests occasionally. We will also have a custom high volume shower system. Looking for 50 to 60 PSI and appx.15 GPM. If the smaller tank is used, I realize a second smaller pump/tank will be needed. I am looking the correct type and size of pump and tank for both cisterns.
Thanx for your time and advice.

mike

I answered this in an email before I saw it here.

bob...

You need to know the flow rate of the large shower PLUS all other water use at the same time. Many showers with body sprays flow at 15-25 gpm. Large tubs at 9-15 gpm; hot only.

And any water treatment equipment like a softener etc. must be capable of a constant SFR (service flow rating) equal to or greater than that peak demand gpm or it can not work correctly.

You might consider finding a way to combine the two systems. One tank could contain treated water, whether hauled in or treated from the rain water, while the other collects rain water that is to be treated.

Your house would be supplied with a single pump and tank system from the treated water tank, while the collector tank would require only a pump that is adequate to operate the filters.

Because the high demands would be supplied by the household pump, the pump on the collector tank would be much smaller. Also, with a low flow rate requirement for treating the water your filter would be much smaller.

Treating runoff requires particulate filtration and disinfection. There should be residual disinfectant in the storage tank so UV is not sufficient. If you use UV it should be supplemented with a residual disinfectant such as chlorine.

Following is a link to a filter that is approved for treating public water supplies to meet EPA requirements. I would use that as a standard for whatever system you select. http://www.harmsco.com/uploads/pdf/harmsco_polypleat_catalog.pdf

I use the PP-BB-20-1 (found in the catalog at the link) as part of a system for treating a roof-runoff-supplied public water system in Maine.

Runoff from a roof can contain a lot of larger material and it is usually more economical to use a less expensive pre-filter to get longer life from the 1-micron cartridge.

You should disinfect any storage system to prevent growth of orgainsms that will inevitably contaminate it. I usually use chlorine from household bleach solution. You can remove the residual cholrine and byproducts with a carbon filter before you use the water.

Rain water is soft and usually doesn't require any other treatment.

You should plan to treat the runoff water as soon as possible after it is collected. That much water will last several weeks and the living organisms in it will make a nasty soup if they are not killed and/or removed. If you use the 10,000 gallon tank as a collector and the 5000 gallon tank is full, then you can circulate the water from the tank and send it back to the same tank. That will clean it up, much as a swimming pool is kept clean. You would maintain a very low level of disinfection in the tank, just above the detection limit.

A 5 GPM pump would be adequate for the filter system and would do both the circulation and feed water to the treated-water tank.

The pump for the 15 GPM shower could be a submersible in the treated-water tank (most efficient) or a shallow well jet pump.

Depending on how much water you expect to collect from one storm, you might want to reconsider which tank is used for collection if that hasn't been precluded by construction considerations.