05:30PM | 07/06/05
Member Since: 09/11/02
13 lifetime posts
I own a double with tenants on each side. There is only one water meter so both are on the same system. But they each have a separate hot water heater. They both say that when the tenant on the OTHER side runs hot water while they are in the shower, their water gets cold. How can one tenant's hot water use affect the other's hot water use? I had new hot water heaters installed when I rehabbed the place 6 months ago.

Jim D

12:10AM | 07/07/05
Member Since: 01/06/01
342 lifetime posts
BeckyG - hi, I'm just guessing here but...if you're feeding both tenants from one water source, after the meter, then the plumber probably put in a Tee connection to feed the hot water tanks. The flow of water out of the hot water tank on either side is affected by the flow of water into the tank. So, when one tenant is using the hot water and the second tenant puts demand on the same water supply, it'll slow the flow to the first tenant. The expert plumbers on this BBS will hopefully let you know if there's other/better explanations for this.

I'd think the solution may require adjustment of the water supply pressure (something to keep it constant) at a minimum...but I'd also think separating their water supply lines (and putting a meter on each) would be the better option. How would you be able to settle a dispute about the water bill between the tenants if one protests an extremely high bill and claims the other tenant let the faucet run continuously for several days, and you only have the one meter? Absent a broken pipe/underground leak, the protesting tenant could make a great case against having to pay anything above his/her average water usage.

I hope the experts can provide you with answers on this. Good luck! Jim D/West Point, VA


07:55AM | 07/09/05
Member Since: 08/29/04
227 lifetime posts
If you are on one street service, what ever water volume coming into the property is fixed. If you use water in either unit there will be a reduction in volume to the other unit, if the service is either too small or corroded by calcium. The same can happen on the main line from the meter to the water heaters. If the line is corroded by calcium, then the volume of water you have will be limited by resistance and size. I have seen 3/4" water lines to the water heaters with a 1/4" inside diameter. When one person used water anywhere in the house, the person in the shower got a reduction in water supply. The first thing to try would be to find out if you have galvanized piping. If you do, then they're probably clogged. If you simply replace them directly from the meter, you will have the maximum pressure and volume available from the service.

If your service is bad (calcium or minerals), then nothing you do on the inside will help. You can test it by checking the volume of water at the meter. If you remove the meter and run the water into a 5 gallon bucket, you can time the filling. This will tell you your flow rate. Most homes should have at least 40 gallons per minute, minimum. But duplexes should have at least 60 gpm. Therefore a 5 gallon bucket should fill up in 7.5 seconds at 40 gpm and 6 seconds for 60 gpm. Pressure is not an issue, you have the same pressure at the end of a 1/8"th inch pipe as a 10" pipe, but a 10 inch pipe has a whole lot more volume. So a main water service could have 65 pounds pressure at the end and the outside diameter could be 1" but the inside diameter could be 1/4" and you'd have no volume, and you'd think there was no pressure.

Finally, if the plumber replaced the water heater, often they shut off the water at the meter. Many times old meter valves get stuck part way open. This effectively leaves the house on a reduced volume, because of the restricted flow from the valve. Old brass valves tended to break very easily. The worst part is you can never tell it happened, because it breaks on the inside. The stem for the valve turns up, just like its supose to (telling the plumber the valve is open), but the disk on the inside stays closed or partially closed. If you have disk type gate valves, have them replaced with full port ball valves.

Raymond VinZant Plumbing Prof.
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