Problem with Gravity-fed Spring

[JasonNC]

Context: We've had a gravity-fed spring for 20 years (no pumps or electricity..all gravity). The spring and the concrete holding tank are about 1,000 feet away up the mountain from our house. I'm not sure about how much elevation gain but it's worked well for us for 20 years so I guess elevation is proper.

Problem: Recently, we noticed that the water pressure is fine for about 30 seconds and then slows to a trickle. Or, if the water pressure is fine in a sink, it drops to a trickle when flushing toilet.

If you wait a while, the pressure returns, only to diminish when you turn it on for about 30 seconds.

Response: I pulled the lid off the concrete tank. It's full of water. It's overflowing over the overflow pipe. We looked to the (not sure what you call it) the output pipe at the bottom of the tank. It appeared to be unclogged.

Possible problem? We're thinking maybe the overflow line is clogged and that blowing it out would help. Does this sound correct?

 

[MicEd69]

Depending on how fast this lower pressure has developed, from your description, it appears the friction drop through the supply line has increased due to a buildup of minerals or a partial blockage.

Did this just happen or was it a slowly developing issue?
What is the size of the supply line?
Do you have a filter that may be partially blinded?
Do you treat the line periodically with chlorine or some other water treatment?

It obviously depends on what the problem is to know if blowing the line out will help.

 

[JasonNC]

Depending on how fast this lower pressure has developed, from your description, it appears the friction drop through the supply line has increased due to a buildup of minerals or a partial blockage.

Did this just happen or was it a slowly developing issue?

Just happened

What is the size of the supply line?

I do not know. Regular sized pipe?

Do you have a filter that may be partially blinded?

I just changed the filter

Do you treat the line periodically with chlorine or some other water treatment?

No.

It obviously depends on what the problem is to know if blowing the line out will help.

 

[RS]

If it happened all of a sudden, I suspect a kink in the line. Or some foreign object got into the line. Is there a strainer in the concrete tank? If you can't find anything obvious, I would blow it out with compressed air, from the bottom up. Are there any joints or access points part way up the mountain?