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Issue No. 142, November 2001, starts on page 84.
While I enjoy do-it-yourself projects like this, there is a serious problem with the system shown in this article. Rainwater off of a roof is not clean due to dust, birds, insects, air pollution, and other contaminants. The UV disinfection system is critical to make this water potable. In a power outage the UV unit will turn off, but the pressure tank will continue to push water to fixtures. This water will be non-potable and could easily make those who drink it sick. It will also require flushing and disinfecting of all water piping each time this occurs.
A positive method of stopping all water flow during a power outage is a must. In addition, UV lamps have a startup time before they become effective. Either a proper timed delay or manual restart should be used after every power failure to ensure this water is disinfected. The state health department may have additional requirements for this type of system.
Scott Dittman, P.E.
Replies
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Scott, thanks for the feedback. You raise an interesting point which I think has validity, and which has me second-guessing myself. Years back, as a builder, two or three of the houses I built had coliform contamination in the wells that direct chlorination didn't fix. The solution, which satisfied the County Health Dept., the buyers, their home inspectors and their mortgage lenders, was UV systems just like what's shown in the article on rainwater collection. Scary to think that so many people never thought about the point that you raise.
Andy
*Dear Scott,Good point, but rest assured that the folks who own these systems (at least the one in the article) are quite aware of the state of the rainwater as it comes off the roof. The top photo on p. 88 (which I took while editing this article) shows the elaborate system of valves and pipes installed to to shut off water from the cistern (manually) and in this case activate a well. I bet a system like the one you describe would be quite costly, especially if you needed a back up power source to shut off the water flow. With the manual system, the homeowner just has to realize that the power is off before turning on the tap. Yeah, the power might go off in the middle of filling the coffee pot or some such, but I doubt that you could convince any of the parties involved to spend the $$$ for that remote possibility. Personally, I think you have a better chance of getting sicker quicker from the stuff that most of us get under the label "potable water" from our taps.Roe
*Roe,Though rainwater cisterns were common place in the old days (my grandparents here in California had one) this system is high maintenance. Many of the components and the cistern itself are great places for bacteria to raise families (not to mention insects and rodents). I think if you showed the system in the article to a knowledgeable health department official, it would be red-tagged. It must have an effective UV system to keep it disinfected. The power could go off during the day while the sprinklers were on and fill the system with unsafe water. If it came back on in a few minutes, you would never know it when you got home. I think at the very minimum you could just add a solenoid valve that would be open when energized (power on) and close (by spring action) when the power went off. This valve should cost a fraction of what the UV system cost and give you one line of defense.I have a house with city water and a cabin with a well. I would much prefer city water any day to a well or a cistern system. Thanks, Scott
*I have a couple of other questions about those cisterns (interesting article, BTW). One: that one was in Texas....what about cold climates, say with a four foot frost line. Do you sink the whole thing deeper in the ground and proceed, or what (soory if that's a dumb question; cisterns are new to me).Two: how long does it take to fill one of those things up....obviously it depends on local rainfall, but that's still a hell of a lot of water to come off one roof? From Roe's post,it seems you have to have a well online also?
*Nope, Adrian, assuming adequate rainfall, you don't need a well too. As to how long it would take to fill one up, I think that you need to do the math. Cape Breton probably gets what, 50 or 60 inches a year? Multiply that by the surface area of the roof, and then apply the factor that converts cubic feet to gallons (or cubic meters to liters -- that's probably easier). I'm not sure, but I think that unless you insulate the cistern, most of it should be below the frostline. Andy
*I wonder if you could come up with a recirculation system to keep it from freezing, kind of like in a pool. Come to think of it, how DO they keep pools from freezing up there?
*I've been using a simple system....stock the pool with buxom starlets, and keep 'em moving, keep those arms a waving. occasioanlly there's a disaster....one freezeup and they're toast.Adrian 'Hef' Wilson
*I like the way your mind works, Hef.
*read the artical... was strange to see it... just as i had read an old "how to homestead" book that i found at a yard sale... had about the same thing but it was built using a site built slip form mounted on a long rod which ran to a center pipe ... you poured a round slab for the bottom then dumping concrete in the slip form hopper pushed it around in circles building up about 7-8 inches a pass... they also showed the same structures for shop, barn and living quarter use... i don't know if they got sick from the water or notpony
*pony: you caused a flashback.... i've used that for cattle water troughs in west virginia. it works.
*I've been enjoying the recent outside-the-box articles (cisterns, building from scrap, etc.). They could help a few folks with similar, unusual constraints (no well or city water; minimal budget and too much time; etc.) Another benefit is that it lets the rest of us examine our assumptions (Can't build if there's no water; must buy from the lumberyard, etc.).My recollection of the cistern article is that was obvious that one should involve an engineer and experienced contractor in the job. Scott, your grandparents clearly lived longer enough using such a system to sire the next generation. I'm impressed that they were able to have UV disinfection so long before it was invented :-). I definitely agree the normally-closed solenoid valve is a good idea as long as fire-protection water is still available during a power failure.I'm unclear what a sprinkler system has to do with drinking water quality. I suppose that the anti-siphon hose bib could be faulty. And then the power goes out. At the same time that the hose end is submerged in a tank of pesticide. At what point do we stop imagining different scenerios? Reasonable people could come to different conclusions. Even reasonable engineers could (Civil PE myself). If a solenoid valve is good, why not a double block and bleed like I use on some fuel-gas manifolds? Do we only protect against single-component failures? Or double? Or triple? I think it varies. I take three source of light when I go caving. But this cistern client sounds like they are actively involved and pretty savy.For infectious stuff, I would have leaned towards chlorination in the first of a two-chambered cistern. Directing flow to, and additional residence time in, the second chamber. If a ppm or so of chlorine (like in muncipal water supplies) was objectionable, then aerate the water as it leaves the cistern.A UV system (or chlorination) does not address heavy metals or pesticides. Either of which can end up on a roof, in groundwater or city water. I treat my city's water myself to remove the 9-36 ppb arsenic. Glad the EPA finally is back on track with that after Shrub's earlier declaration that arsenic is a vegetable. So I'm definitely one of those people Roe refers to who would be safer drinking untreated rainwater than untreated city water.Jim: Never occurred to me to have a pool in snow country. But what I've seen other people do is drain some or all of the pool in fall (can't drain it all if the water table is high). If they leave water in it, they throw in inflated innertubes to take up the compressive forces from ice formation. But call a pool guy from the Minneapolis yellow pages to find out for sure.Adrian: Four-foot frost depth? (My water line runs in at 11 feet for a reason!) Definitely makes it a tougher project. Burying it deep enough would be one approach. I'd probably throw in a circulator pump and an air-to-water heat exchanger to use free summer heat to get the water to 70 or 80F going into fall. And a thermometer and some way to add heat mid-winter if necessary. Those added costs may well be a deal-breaker unless it is a really nice property. Warmer incoming water does save a bit on utility bills in the house.Andy: I've wanted to see someone build two cisterns in their basement or sub-basement. Both insulated. One kept hot (through solar, wood, or whatever) and the other left cold. Then demands for heat (hydronics, bath, towel warming, etc) and cold (A/C, refrigerator) could be met with 100-watt circulator pumps. Yeah, I know, it's so 70's (like cisterns and lumber scraps). But like you, I spent the 70's with pimples so I only caught the tail end of solar, etc in the early 80's. And we have so many more neat, really cheap electronic controls now. -David
*Dave, I remember reading in, I don't know, Popular Science?, in the 70's about a building at, Princeton?, that was cooled in the summer by parking lot snow pushed into a big pit. I've always loved stuff like that. Tidal hydroelectric is another favorite.Andy
*Tidal exchange in Cook Inlet (on which we have 700 feet of sandy beach) is as much as 40 feet vertically. Second highest in the world after Bay of Fundy. Every year a couple of people die when the tide comes in faster than they expect.I saw something on creating a big pile of snow for the purpose of summer A/C. More recent than the 70's. Wasn't a big enough pile. The obvious approach to me (cause all my professional work is about the subsurface) is to freeze a big chuck of ground. Circulate antifreeze in the winter. Let the soil moisture go to ice. About 10 feet of overlaying soils would be lots of cheap, pre-installed insulation.You know the indoor climbing gyms? Any interest in a one-page article on an artificial, outdoor ice-climbing pinnacle? I've been threatening to run a garden hose up a 80-foot spruce for a while now. -David
*David -- I talked to my dad about my grandparents cistern. They never drank any of that cistern water, only washed clothes in it because it was softer than the well water. Fundamentally, the system described in the article is unsafe. It must have the UV unit irradiating the water to kill bacteria to not poison themselves. The reference to the sprinklers is as follows -- if the sprinkler timer comes on (mine always have a battery backup) when the power is off, the pressure tank will push cistern water past the UV unit into the household plumbing. This water is not irradiated and thus will have live bacteria. The Mrs comes home with the kids and they drink the water from the tap, not knowing what has gone on. When the kids are sick later they think its food poisoning or the flu. The filters in their system will remove particles, but every one of those will come with a written warning saying they don't make non-potable water drinkable.There were some other good points on the cistern system made in the letters to the editor printed in the current issue.Arsenic in the parts per billion range that the EPA is talking about is a waste of tax dollars to treat. And I make my living working on water treatment plants! I would rather see them spend $500 million helping homeless people than catering to special interests. My 2 cents. Thanks
*I see what you were referring to regarding sprinkler usage. I thought 1) sprinkler have backflow preventers on them but that is not an issue in your scenerio, and 2) gardening water would be taken off before the UV unit. The advantage would be that less water is treated and filtered and the system doesn't need as much service and kwh. The downside is that kids would have to be cautioned to not drink from the garden hose. Of course all those Hawaiian cistern systems have none of these safeguards. And most of those people survive. Just like arsenic - MOST people survive it. Arsenic is estimated to cause between 6 in 1,000 and 1 in 10,000 risk of additional cancer from drinking in communities with elevated levels. That's a less risk than some people take on willing (1 in 3 for smoking, 1 in 10 or 1 in 100 for a lot of lifestyle choices). But far greater than the 1 in 100,000 or 1 in 1,000,000 that are more common guidelines for most involuntary risks.I disagree that "special interests" are causing that regulation. I'd say the most vocal special interests (rural water districts) have been arguing that their customers would rather drink carcinogens than spend $38 to $350 more a year for treatment. Having already had skin cancers removed (one type of cancer which arsenic elevates the risk of), I suppose I'm a special interest. But I'm less aware of an organized lobbying effort for my benefit. -David
*You guys...just want to say, I luv ya. Having a Breaktime moment. Will be rereading this stuff tomorrow.Goooodddd.....
*ScottThe battery backup in the lawn sprinker is for the clock unit. It won't supply enough power to operate the valves.
*Bill,Right you are. I talked about the sprinklers but really any use of the water system -- sinks, toilets, etc. will bring non-potable water into the drinking system.David - The arsenic levels are subject to debate as are EPA estimates on what it costs. We can design systems to make water as pure as you want but we are faced with the nagging problem that most water is used for irrigation, flushing toilets, etc. The capital costs will make bottled water the most attractive alternative. The special interests are the environmental and some consumer groups who always lobby for the most restrictive criteria. Fortunately for them, they don't have to find (tax)the money, design, and construct what they envision. I'm not complaining though!
*Wife and I stayed on a funky island in the Bahamas, where almost all the water was supplied by cisterns. I never saw a filter at the house we rented, drank the water for a week, the only effects were wild cravings for rum...An American from Colordo gave us a tour of the house he was building down there...the construction was amazingly solid(hurricanes)and his cistern system was something like six one thousand gallon plastic tanks filled through a huge filtration system connected to his gutters, and for backup he had a reverse osmosis machine to make sea water potable. This guy was covering all the bases...
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Issue No. 142, November 2001, starts on page 84.
While I enjoy do-it-yourself projects like this, there is a serious problem with the system shown in this article. Rainwater off of a roof is not clean due to dust, birds, insects, air pollution, and other contaminants. The UV disinfection system is critical to make this water potable. In a power outage the UV unit will turn off, but the pressure tank will continue to push water to fixtures. This water will be non-potable and could easily make those who drink it sick. It will also require flushing and disinfecting of all water piping each time this occurs.
A positive method of stopping all water flow during a power outage is a must. In addition, UV lamps have a startup time before they become effective. Either a proper timed delay or manual restart should be used after every power failure to ensure this water is disinfected. The state health department may have additional requirements for this type of system.
Scott Dittman, P.E.