The water in your area ranges from moderate to medium hardness. This mean that the hard miinerals coat the heat exchangers and cause failure sooner than in soft water areas.
Constituent Range MCL
Calcium (ppm) 32 – 49
Chloride (ppm) 14 – 50 250
Magnesium (ppm) 2 – 9 Not Regulated
Sodium (ppm) 12 – 35 Not Regulated
pH (units) 7.98 – 8.75 6.5-8.5
Bicarbonate (ppm) 79 – 148 Not Regulated
Carbonate (ppm) 0 Not Regulated
Total Hardness as CaCO3 (ppm) 89-156 Not Regulated
Total Alkalinity as CaCO3 (ppm) 65 – 121 Not Regulated
Phenol Akalinity as CaCO3 (ppm) 0 Not Regulated
Total Dissolved Solids (ppm) 137 – 255 500
Conductivity (mmhos/cm) 264 – 515 Not Regulated
Water Hardness Guide
Milligrams per Liter Grains per Gallon
or Parts per Million
Soft 0 to 60 mg/L 0 to 3 1/2 gpg
Moderate 61 to 120 3 1/2 to 7
Hard 121 to 180 7 to 10 1/2
Very Hard over 180 over 10 1/2
Source: American Society of Agricultural Engineering
Tankless, or instantaneous water heaters, have small tubes that collect hardness to clog the exchanger. This is not a problem for Europe, where the Bosch unit is used extensively, because it is common practice for the factory technicians to come to the home to disassemble and clean the units. It is acceptable there to replace the exchanger or entire unit once in five years.
This is not a common practice in the US. Such units work well in flows greater than 1/2 a gallon per minute. When flows are low, as in a draw for a pot of water, the firing rate is less stable.
“Demand Water Heaters
It is possible to completely eliminate standby heat losses from the tank and reduce energy consumption 20% to 30% with demand (or instantaneous) water heaters, which do not have storage tanks. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed. With these systems, you never run out of hot water. But there is one potential drawback with demand water heaters — limited flow rate.
Typically, demand heaters provide hot water at a rate of 2 to 4 gallons (7.6 to 15.2 liters) per minute. This flow rate might suffice if your household does not use hot water at more than one location at the same time (e.g., showering and doing laundry simultaneously). To meet hot water demand when multiple faucets are being used, demand heaters can be installed in parallel sequence. Although gas-fired demand heaters tend to have higher flow rates than electric ones, they can waste energy even when no water is being heated if their pilot lights stay on. However, the amount of energy consumed by a pilot light is quite small.”
One good reason to install an instant water heater is that one line would suffice for a bathroom supply, which could be branched for hot and water supply. In this case, the hot and cold water pipes are already in place.
For small flows from the sinks, an electric instant water heater at the point-of-use would suffice.