We are promoting rainwater harvesting in Guatemala. Water analysis indicated that the harvested rainwater has a lower pH value than what the U.S. Environmental Protection Agency suggests. They say water pH value is a secondary drinking water standard and recommend a pH between 6.5 and 8.5 for drinking water.
The pH of the harvested rainwater in our area varies between 4 and 5.
Are there any negative effects on the human metabolism drinking water with low pH level? Can we slightly increase the pH level by any household water treatment methods?
Rain water has few if any minerals and hence very little buffer capacity.
to determine normal rainwater pH
First, we calculate the amount of CO 2 dissolved in water under an atmosphere of pressure from Henry’s Law
Since CO 2 makes up 0.0355% of the atmosphere (on the average) and
K CO 2 =2x10-3
Since is in equilibrium with H 2 CO 3 (aq), the first acid equilibrium is normally given by
is predominant. Also since
CO 2 (aq) + H 2 O « H + (aq) + HCO 3- (aq)
The proton and bicarbonate concentrations are equal. Thus
When we substitute the carbon dioxide concentration, and solve for pH, we get
p H = 5.65
Since rain is in equilibrium with the atmosphere, this is the pH expected for natural rain. It is also the pH expected if the body of water is in equilibrium with the atmosphere, and does not contact limestone (e.g., CaCO 3). Adding some limestone to your water tank should increase the pH overtime and restore proper balance.
Yours is a bit lower than 5.65 so it may contain some sulfur compounds forming a bit of sufluric acid but shouldn't be harmful.
Drinking treated rainwater might be the only solution for several parts of India in the coming years. Some of the traditional harvesting systems in the rural Rajasthan and Gujarat have worked very well. the "tankas" collect rainwater from rooftops and channels that are painted with limestone slurry. Water passes through a thick layer of sand before percolating into stone lined wells. Water stored in such tanks stays potable and surprisingly tasty.
Hi Sharon: Rainwater reuse as drinking water would be OK but the water should be modified by adding electrolytes since it will typically be electrolyte poor. You should be able to add this to the water by a simple injector or by putting the collected water into a reservoir holding tank and adding electrolytes manually. Drinking water with a low electrolyte concentration for a long period or time i.e., as the primary supply source would be bad for health. By the way adding the electrolytes will also adjust the pH to within the range of the recommended US EPA range. Really only end trace amounts of micronutrients and overall pH can be adjusted using calcium carbonate. Hope that helps.
Another important issues is the leaching effect of acidic water, acidic water has corrosive properties, it leaches substances from everything its stored in and flows thru, plastic storage containers and PVC pipes are all made of toxic materials.
Yes, their are household treatment methods to increase pH, but of equal importance is complete purification. www.truestspring.com nevin@truestspring.com
my friend,you are the best. i want to returned your all struggle effort ,grind by nature produced in the molecule as a Perspiration ,i want to exchanged your perspiration in to dollar's ,this is a happy news for you all.
It may be better to let first showers not be collected for a few minutes as these will have maximum acidity. For balance rain water, you may need to add a few minerals/ sodium/ potassium/calcium salts in traces as they do mineralisation of RO water..to make Ph as well as mineral salt content better for water to taste good as pure RO water without minerals is also bitter. Must also check Rainwater for any microbes that float in air and come down with rain.
Low pH of the rain water is usually caused by air pollution. We had the same problems in the 80s and 90s of the last century here in Germany. We called it "acid rain". It can destroy trees and whole forests. The reasons are sulphur oxides and nitrogen oxides from traffic, industries and power plants who don´t have sufficient exhaust gas treatment plants. The gaseous pollutants react with the humidity in the air to sulphurous acid and nitrous acid which leads to a low pH in the rain water. The low pH in the rain water can be adjusted by using Calcium Carbonate or Dolomite filters. They remineralize the rain water with Calcium and / or Magnesium and increase the pH at the same time. But you should be aware that the sulfate and sulfite as well as nitrate and nitrite anions are still remaining in the water. Especially nitrite is toxic and for nitrate there are limit values given for the use as drinking water. So please make water analysis before you use this water as potable water. If there is nitrite in the water you cannot drink it. I don´t know the limit value for nitrate in drinking water in your country. Here in Germany the limit value is 50 mg/l. Lots of experts think that this value is still too high and should be lowered.
