"No, that's our cistern." I would respond.
"Cis...stern?"
In most cases it wasn't that these people hadn't ever heard of a cistern before but just couldn't understand why someone in this day and age would ever install one. I may as well have told them I was installing a water-wheel or treadle loom. Some of the concerns we had that led to the decision to install a rainwater collection system and cistern are as follows:
- Our existing well is slow to recover (only 1-2 gal/hr) and produces sometimes stinky, hard water that will tarnish silver jewelry.
- Because our well was drilled to a depth of 300', the water is only accessible with a strong (3/4 h.p.) submersible pump - no grid power = no water.
- Drilling or digging a new well is expensive and risky - there's no guarantee of finding water that is any more abundant or of higher quality than what we already have.
- Wells can be contaminated - even if you take good care of your well, someone (ie agriculture, industry or some ignorant neighbour) further "upstream" the water table could introduce contaminants.
Rainwater collection addresses these concerns in that it is renewable, high quality water that can be safely stored in isolation and accessed by hand pump if necessary.
Calculating an ideal amount of water storage for an entire household is tricky - there are a lot of variables. I once did a "back of envelope" calculation for the ideal amount of storage capacity for our home and came up with a figure of approximately 10000 gallons. Because of budgetary limitations, I decided on a 2200 gallon poly tank. This is not quite 25% of ideal but we (as a family) tend to be quite conservative with our water use already and if required, I can always set the well pump to "trickle fill" the cistern.
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| To install the cistern, I had a pile of sand made where I wanted it to go on the gravel pad. We lowered the tank with the excavator until it was at the right elevation relative to final grade, then built the sand pile up under the tank with shovels. Later when the foundation and tank were backfilled, I filled the tank with water to off-set the weight the backfill. |
Really finding your blog informative. A couple of questions on the cistern. Does the cistern have to be completely below the frost line in order for the water inside not to freeze? What will you be using for water in the winter (I'm assuming your rainwater harvesting is coming off the roof)?
ReplyDeleteHi Fred,
ReplyDeleteThe cistern has 4" rigid XPS insualtion covering it which will raise the frostline up to somewhere near the foam - depending on how cold it gets. Snow will help a bit as well.
As far as collecting water in the winter, that is a good question. If future winters are as mild as this year, I may be able to collect water off the roof year-round... Otherwise, my other options are:
1. Run a line from my well and set the well pump to operate off of a float switch.
2. Have water hauled in by tanker (I don't see myself going this route).
3. Eventually do some experimenting with a solar thermal snow-melter...
Thanks for responding. If you ever come up with any ideas for a solar thermal snow-melter, I hope you blog about it. I'll be building next year and I really want to avoid having water hauled in.
DeleteLucas and Fred,
ReplyDeleteA bit of trivia. One inch of XPS, below grade, is equivalent to about one foot of soil coverage. Therefore, four inches of XPS would be similar to burying the cistern with four feet of cover fill, as long as the layer of foam is wide enough that the frost does not penetrate from the side. - Jim