We "shock" treat (50 ppm) the water system (with hot water heater bypassed) once a year in the spring and then maintain normal free chlorine levels (1-2 ppm) the rest of the year. We check the free chlorine levels using test strips (0-10 mg/L, same as 0-10 ppm by mass). They are readily available at pool supply or Spa stores, as well as Walmart, Lowes, etc. ($10-15 for 100 strips). They typically test pH as well. We test the water prior to filling our tank to see if we need to add chlorine, or not, and how much.
Free chlorine levels in drinking water need to be at least 0.2 ppm to be effective as an antimicrobial and no more than 4 ppm for normal situations, according to the EPA and WHO. In an emergency situation 10 ppm for questionable clear tap water; 20 ppm for questionable, cloudy tap water (30 minutes contact time prior to drinking). Contact time, temperature, pH and sensitivity of the microbe all determine how effective the level of free chlorine is at inactivating the pathogens. If you are really worried, 4 logs of viral inactivation and 3 logs of Giardia inactivation can be had with a contact time of 6 hours at 1 ppm free chlorine, under the least favorable conditions with normal tap water. Basically, fill, treat and use it from the tank the next day. Most of the typical microbial contaminants, if present at all, are inactivated within 30 minutes.
The amount of free chlorine becomes less over time after oxidizing various organic molecules and microbes in the water. High levels of iron and manganese in the water also reduce the free chlorine level. To answer the question "is the water still good to drink or avoid growth?" just use a test strip to determine if the free chlorine level is still within the effective range.
About half of the people can smell chlorine around 1 ppm. We aren't sensitive so we keep ours at 1-2 ppm
Normal bleach is made by bubbling chlorine gas into a sodium hydroxide solution, so the solution is very basic (corrosive) as well as oxidizing. Normal bleach is ~5.25% chlorine (AKA sodium hypochlorite) or 52,500 ppm.
ppm levels for various applications:
hospitals use a 20% bleach solution (10,500 ppm) for sanitization of hard surfaces
Shock treatment of water wells uses a 2% bleach solution (1,050 ppm)
Beer and wine industry use 1% bleach solution (525 ppm) to clean and sanitize equipment. Food service companies use around 200-300 ppm for food contact surfaces and up to 800 ppm for sanitizing equipment.
Shock treatment of RV systems - 50 ppm (3.6 mL bleach per gallon of water desired). Typical conversion 5 mL = 1 tsp; 15 mL = 1 Tbsp; 29.6 mL = 1 oz (2 Tbsp). Dilute the required amount in a reasonable volume and pour it in your water tank and then fill the rest of the tank with water. You can use high range test strips (or a five fold dilution of the sample) to verify the free chlorine shock level at each tap (or just the one(s) at the end of the pipe run(s)). After a contact time of your choice (typically 15 to 30 minutes, it is sanitized, but the level of free chlorine needs to be reduce before you can drink out of the system.
Two drain and fill cycles is usually enough to reduce the chlorine levels to less than 4 ppm, if you take your time during the drain portion. You are ready to go camping and can drink the water. Easy to to show you are within a safe and effective range with the test strip.
Targeting 1 ppm or less uses very little bleach and is more difficult to measure. Easy to make up a diluted bleach stock solution (1 cup and then add water to make it a gallon). This 16 fold diluted bleach stock solution is 3,281 ppm. Use 1.14 mL of 16x diluted stock per gallon of water to treat, to achieve 1 ppm final.
'05 Ram 3500, 4x4, DRW, LB, 6spd man, CTD, PRXB exhaust brake, Roadmaster bar
'01 Corsair 10'8" - 4,200 lbs., Xantrex XADC 80A, Link 20, 4-Lifeline GPL-4CT, PowerGate Isolater, 2 AWG wire, PI 30A EMS, 2 Honda EU2000i, parallel kit, ext. duration tank.
