Head and Pressure units

In solar pumping systems, Head is usually expressed in units of Level difference [meter or feet]. The pressure at the basis results of the water column weight.

Physically, passing to pressure units involves multiplying the height by the water density (1000 kg/m³) and the gravitation constant (g = 9.81 m/s²). And for getting [bar] we have to divide by 100'000 [Pa/bar].

In summary, we have the following equivalences:

1 Pa = 1 N/m² (mksa basic unit)
1 bar = 100 kPa (definition of the Bar)
1 bar = 10.19 mWater (passing from level difference to pressure)
1 bar = 33.44 ftWater (Idem)
1 bar = 2088 lbs/ft2 (Pounds/Square feet)
1 bar = 14.504 PSI (PSI = Pound/Square Inch)
1 bar = 0.987 atm
1 bar = 750.1 torr or mmHg

1 mWater = 0.0981 Bar
1 ftWater = 0.0299 Bar
1 PSI = 0.069 Bar