Building a water tank

Hi guys,

I'm purchasing a land in the Himalayas India. The land is on a slope and there is a water spring above the land from where I want to take my water.
My idea is to build a water tank that will take water from the spring and return the surplus back into the little stream below.
I've two basic questions.
1. I was told that there is a lot of sand in the water so I'll need a good sediment filter and also to clean the tank often. I want to design the tank in such a way that the sand will sink to the bottom and won't enter the pipe. Is anyone has some insight about this?
2. How do I calculate the water pressure? I guess it is a function of the elevation and the size and length of the pipes. Any help will be appreciated

Thanks,

P.S. This is my first post here, so forgive me if I'm doing something nubish. I know that this forum is about collecting rainwater, but I didn't find any forum dealing directly with the topic in question.

I would build 1 big tank like you are envisioning and then put a sediment filter before that, which could be a home made sand filter.

Hi Swami, welcome to permies!

It's possible that your post would also fall under the natural building heading, but I don't see anything wrong with having it here. All water is rainwater at some point, right?

Regarding your questions:

1) It should be possible to have much or most of the sand settle out, but this depends partly on how fine it is; I would think you'd still want a filter. I'm by no means an expert in this, someone with more experience may have a better solution... but I'd approach this with small settling tank/sand-trap prior to the main tank, with the springwater entering at the bottom and leaving at the top; the pipe leaving the top would go through a filter, then into the main tank, and travel to near the bottom. Then, water would leave the main tank from a pickup near the top of the water, via a floating pump as is common for pond irrigation. I've roughly sketched this for clarity, see below.

The same sort of idea could be applied to an in ground reservoir pond, with a smaller pond leading into the larger one to slow the water and catch sediment where it is easier to remove; I think this is fairly common practice.




2) As far as pressure goes, you probably want to convert the feet of head, which is simply the height of the tank above where you are using the water, into PSI. This is simple, about 0.433 PSI per foot of head. Then you would need to deduct the losses from the size and length of the pipes, which is less straightforward as it will change depending on the flow rate... You may be able to just rely on rule of thumb for the pipe sizing, but that will depend on how much pipe you need to run, and how exacting your pressure and flow requirements are.


Have you already decided what method will be used to build the tank? How big will it be?

Bengi and Dilon you are the best!

Thank you very much.

Couple of points:
1. This is India. Can't depend on electricity for a pump. Everything should be mechanical.
2. I didn't understand exactly how the biosand tank works, but I can figure it out myself.
3. I don't need/want a float valve. It is enough to leave an open pipe that returns the surplus water to the stream.
3. I haven't decide about the material for the tank. The normal usage here is either cement tank or a ready made plastic tank. I'm more inclining towards the cement solution, but open for any suggestion.
4. The tank is going to serve initially only 2 people in a humble house. I want a good water pressure, but it need not be crazy. I've no idea what is the average PSI in the West.
5. The tank is going to sit about a 100ft away from the house, and about 20-25ft above the level of the roof (this is a very rough estimation. I need to check it next time I go there).

Maybe solar? Check this out:

Hi! Where are you?

If you're in a place with hard freezes like here in Ladakh, then a concrete tank is liable to crack due to water freezing and expanding in the pores. Yah, I don't plastic much, but then again the reputable-branded plastic water tanks are probably food-safe, water-safe, non-reactive, especially at the cold temperature of spring water and if you keep direct sun off it. They're more reliable than concrete tanks, in my experience.

For sand, you need a simple settling tank, not necessarily a filter. In order to make the water drop most of its sand, you need a settling tank where the water comes in, slows down, drops its particles, and quietly and gently moves on down into the pipe system.

-- A good way is to have the inlet and outlet of the settling tank both up high.

-- Then an overflow pipe even higher, and it should be bigger diameter than the inlet pipe in order to be failsafe in case the inlet pipe is rushing in at high volume someday. This overflow pipe should outlet to a canal that directs the water back to the local stream, as you wanted.

-- The bottom will fill up with with sand so you have to design the clean-out system from the beginning. The very lowest point of the tank should have an outlet with a valve that you can operate from outside the tank, that outlets towards the stream. Whenever the tank needs to be cleaned, you open the bottom gate-valve, and reach in from the top with a stick or a broom and flush all the sand and junk down the clean-out hole. Design it so that you can reach the bottom with a commonly available tool. If your clean-out hole is half an inch above the very bottom, you'll spend an extra half hour flushing clean water through to get it completely clean, so try to really have it at the very very bottom spot.

-- Our settling tank is long and skinny, a concrete canal about 1.5 feet wide, 2 feet deep, and 25 feet long. It has never been totally waterproof, has always leaked from the bottom into the nearby stream, and then in winter those leaks grow, and we have to rebuild it every few years. And since it's right next to the stream, floods keep eroding the stream-bed out from under it. It's not going to last much longer, I'm afraid, but we have a new water source (borewell) so we'll give up on this one eventually.

-- If you don't have hard freezes, cement might be fine. Hire some good guys to do it, though -- this isn't really the place to learn do-it-yourself plastering skills.

-- If you get hard freezes you have to bury all pipes and connections. Insulating them is a very poor second choice, and should be saved for connections that can't be buried. The idea of burying pipes to prevent freezing is something that people in India (including plumbers and high level officers in the Air Force engineering division) have a lot of trouble with. They either don't believe it works, or they do it halfway and suffer broken pipes.

If your spring is above the house, you shouldn't need a pump. Americans are dependent on water pressure for their showers and other appliances. For you, if you don't get good water pressure, you're probably happy with bucket showers, right? Our water system here has very little pressure, and it's fine for us. The top of the storage tanks (Sintexes) is only two or three feet lower than the spring's settling tank, which is about 500m away, but it slowly and steadily fills the tanks. The pipe is buried 3 feet deep to prevent freezing. The bottom of the storage tanks are just 7 feet higher than the bathing block. When they tanks are full, the shower heads give some pressure, but the fact is most of us prefer to take a bucket of warm water from the solar water heater instead.

The sand problem is easy. Simply install your use pipe a few inches off the bottom of the tank.

Check http://ferrocement.com/tankBook/indici.en.html for the english .en version of ferrocement tank construction

Build your tank with a sloping bottom (gentle slope)  Put a large diameter drain at the bottom of the slope, like a bathtub, cap the other end of the drain pipe with a threaded cap that seals well, or use a large ball valve, etc.
Make your normal outlet pipe draw water from 5-7 cm above the drain pipe.

The sand/sediment will tend to flow down the slope toward the drain.

Periodically open the drain pipe to let out the sand/sediment.