Water tank gravity feed: how and what

beowulf · May 23, 2006

Apparently the pump for my well went out (other causes have been checked and eliminated ) so we have had no water for 4 days - it is supposed to be repaired in a day or two. It was put in in 1987 about 450 feet deep. Anyway, having no water got me to thinking: at times we have no electricity and thus no water. I thought I could plumb a poly sealed tank with a separate line and valves so I could run the water I use for plants and outlying bibs through the storage tank, but continue to use the bladder pressure tank for house water. I would however plumb it so I would have the ability to cut that off and divert the tank water to the house when electricity was out - the tank would be the reserve. Many questions however:

1. How much higher than the house floor would the tank need to be to ensure sufficient pressure from the gravity feed? I have terraces right behind the house so can easily put the tank about 4 feet higher than house ground level, or if up one more terrace, about 8 feet higher. At some distance back - about 50 feet I could go maybe 15 feet higher. I can build any of the terraces up using tractor as no shortage of dirt.

2. As this is well water (very good mountain water) it is not treated with anything. Will I have problems with the water in the storage tank going "bad" in some way if it sits there a while - we would not be using the tank water much in winter? Now the water goes direcctly from the pressure-bladder tank to the house.

3. I intend to run the inlet to the top of the tank and of course, have the storage tank outlet at the bottom, using a three-quater inch line. I assume there will be enough pressure to keep hot water heater flowing. Anything else I need to know? Any preferred size, shape of tank?

4. At times we hit below freezing. We then keep water dripping at a faucet in the house to keep the water flowing thru the bladder tank and pipes to prevent freezing. What could I do to protect the storage tank?

Any help or information will be much appreciated.

beowulf · May 23, 2006

Apparently the pump for my well went out (other causes have been checked and eliminated ) so we have had no water for 4 days - it is supposed to be repaired in a day or two. It was put in in 1987 about 450 feet deep. Anyway, having no water got me to thinking: at times we have no electricity and thus no water. I thought I could plumb a poly sealed tank with a separate line and valves so I could run the water I use for plants and outlying bibs through the storage tank, but continue to use the bladder pressure tank for house water. I would however plumb it so I would have the ability to cut that off and divert the tank water to the house when electricity was out - the tank would be the reserve. Many questions however:

1. How much higher than the house floor would the tank need to be to ensure sufficient pressure from the gravity feed? I have terraces right behind the house so can easily put the tank about 4 feet higher than house ground level, or if up one more terrace, about 8 feet higher. At some distance back - about 50 feet I could go maybe 15 feet higher. I can build any of the terraces up using tractor as no shortage of dirt.

2. As this is well water (very good mountain water) it is not treated with anything. Will I have problems with the water in the storage tank going "bad" in some way if it sits there a while - we would not be using the tank water much in winter? Now the water goes direcctly from the pressure-bladder tank to the house.

3. I intend to run the inlet to the top of the tank and of course, have the storage tank outlet at the bottom, using a three-quater inch line. I assume there will be enough pressure to keep hot water heater flowing. Anything else I need to know? Any preferred size, shape of tank?

4. At times we hit below freezing. We then keep water dripping at a faucet in the house to keep the water flowing thru the bladder tank and pipes to prevent freezing. What could I do to protect the storage tank?

Any help or information will be much appreciated.

CurlyDave · May 23, 2006

For every two feet of elevation you get about 1 psi minus the friction loss in the pipe. Most household systems run in the 30-50 psi range, so you would need something on the order of 60 feet of elevation. Less would be OK if you were willing to accept lower flow rates during a power outage.

If your house is close to the well, you might want to consider a generator instead of a storage tank.

Not only will you have water, you will also have enough electricity to run lights, reefer, TV, etc.

If you go to the trouble of installng a tank at a sufficient elevation to give good pressure, you should be able to do away with the pressure tank and just use a float switch in the tank to control the well pump. This will keep your water changing and fresh in the tank.

CurlyDave · May 23, 2006

For every two feet of elevation you get about 1 psi minus the friction loss in the pipe. Most household systems run in the 30-50 psi range, so you would need something on the order of 60 feet of elevation. Less would be OK if you were willing to accept lower flow rates during a power outage.

If your house is close to the well, you might want to consider a generator instead of a storage tank.

Not only will you have water, you will also have enough electricity to run lights, reefer, TV, etc.

If you go to the trouble of installng a tank at a sufficient elevation to give good pressure, you should be able to do away with the pressure tank and just use a float switch in the tank to control the well pump. This will keep your water changing and fresh in the tank.

AchingBack · May 23, 2006

As an example, a tank of water located 115 ft. above your ground floor would give you 50 psi. Half of that height would give you 25psi. Half of that, and you are now at 12.5psi. Its up to you to decide how much pressure you need. The higher the tank, the greater the pressure. The size of the tank depends upon how much water you think you will need to store. Shape isn't an issue. Make sure the tank block out sunlight to discourage algae. I would try to find one that is insulated, or else build and enclosure and insulate it yourself.

As for the 3/4" line, it will allow a flow of approximately 12 gpm, depending upon the type of pipe used. The larger the diameter, the greater the flow. A 1" pipe would deliver closer to 20 gpm, depending upon the type of pipe.

AchingBack · May 23, 2006

As an example, a tank of water located 115 ft. above your ground floor would give you 50 psi. Half of that height would give you 25psi. Half of that, and you are now at 12.5psi. Its up to you to decide how much pressure you need. The higher the tank, the greater the pressure. The size of the tank depends upon how much water you think you will need to store. Shape isn't an issue. Make sure the tank block out sunlight to discourage algae. I would try to find one that is insulated, or else build and enclosure and insulate it yourself.

As for the 3/4" line, it will allow a flow of approximately 12 gpm, depending upon the type of pipe used. The larger the diameter, the greater the flow. A 1" pipe would deliver closer to 20 gpm, depending upon the type of pipe.

bebster · May 28, 2006

If the problem was the pump failed, seems to me a lot of work for a backup to something that happens maybe once per 20 years. What would it cost to put in a second well? Around here we just dig down 50' through sand and find water! I don't think it will be practical to store water high enough and clean enough for you to be pleased with that solution.

If the problem was a power outage, then a generator would be a better solution, since you can solve other problems other than no water. That's what I'm doing -- that way the food in the refrig doesn't spoil, the family can still watch TV, etc. etc.

bebster · May 28, 2006

If the problem was the pump failed, seems to me a lot of work for a backup to something that happens maybe once per 20 years. What would it cost to put in a second well? Around here we just dig down 50' through sand and find water! I don't think it will be practical to store water high enough and clean enough for you to be pleased with that solution.

If the problem was a power outage, then a generator would be a better solution, since you can solve other problems other than no water. That's what I'm doing -- that way the food in the refrig doesn't spoil, the family can still watch TV, etc. etc.

rambler · May 30, 2006

I have 1.25" pipe gravity feeding my cattle. Probably operates on 5-15 lbs of pressure - depending on how full the underground cistern is.

With only 10-15 foot of fall, you will need much bigger pipe than 3/4". Way too restrictive for gravity feed.

It gets to minus 30 degrees here and can be over 30 days with never getting above freezing, so water stored above ground just doesn't compute here - don't know what you consider 'cold' weather there. Water lines need to be 5 or more feet deep.

--->Paul

rambler · May 30, 2006

I have 1.25" pipe gravity feeding my cattle. Probably operates on 5-15 lbs of pressure - depending on how full the underground cistern is.

With only 10-15 foot of fall, you will need much bigger pipe than 3/4". Way too restrictive for gravity feed.

It gets to minus 30 degrees here and can be over 30 days with never getting above freezing, so water stored above ground just doesn't compute here - don't know what you consider 'cold' weather there. Water lines need to be 5 or more feet deep.

--->Paul