Monthly Archives: September 2013

Drinking water on the cheap

Anyone who goes backpacking knows that suitable water can be hard to find.  Contaminated water can make for serious health problems. For those areas where people live with contaminated water, the problem is compounded, as children have significantly higher mortality from diarrheal illnesses.  Many of these places lack the resources to implement costly solutions to this problem.  This paper looks at a relatively inexpensive way to purify water. As a significant component of wilderness medicine is improvisation, it is applicable in survival situations as well.

The authors attempted to answer multiple questions.  The first was simply, can solar water disinfection (SODIS) work with the contaminated water from a large city in Pakistan? Second, are there ways to increase the efficiency of the SODIS system?  Third, to what effect does the intensity of the sunlight affect disnifection?  Fourth, how much plasticizer leaches into the water with heating?  Their materials were locally made PET bottles, natural sunlight, the rooftop of the building, and foil and black paint.

The untreated water had 827 CFU/100mL of total coliforms, with 82.3 CFU/100mL of fecal coliform.  With all 3 types of vessel (transparent, reflective with foil, and absorptive with black paint), 90% of total coliforms were inactivated within 4 hours.  The absorptive vessel had the highest temperature attained, and also had the most effectiveness for removing coliforms in strong sunlight, while the reflective worked best in weak and moderate sunlight.  They also determined that the amount of plasticizer present after heating was significantly lower than the WHO guideline value for safety.  Even if it weren’t, in a pinch, a single dose of DEHP is less toxic than known enteric pathogens.

This paper continues the trend of showing the efficacy of using passive solar disinfection to make safe drinking water.

Application of solar water disinfection for treatment of contaminated public water supply in a developing country: field observations.

Palm cooling, effective or not?

RTX cooling, or Rapid Thermal Exchange, started with two Stanford researchers in the 90s looking at rewarming patients after surgery.  The basis is that mammals have arteriovenous anastamoses in the palms and soles, and this can be used to bring high volumes of blood in contact with a thermal plate.  A small vacuum is created in the device to further increase blood flow.  The inventors received a DARPA grant to study the device for possible military use.  It came into vogue in the athletic and wilderness fields as an easy and effective way to decrease or increase core temperature.  A secondary benefit of increased endurance was noticed in some trials, and this is being looked at by a few.  Currently devices are in use by many sports teams, including the San Francisco 49ers.
The curious thing is, if you look through the 9 studies available on pubmed using palm cooling as the search, you’ll notice not all of them are positive.
The positive studies are authored by:

The negative studies are authored by:

Certainly sample size in all of these is low, and perhaps the device is effective at cooling and/or endurance increase.  However, based on the literature available, it is 5 in favor, 4 against.  Then consider that 2 of the 5 positive papers are written by the owners of the patent for the device (Grahn and Heller).  I would wait to purchase one of these devices for my personal gym.