Among the rustic charms of off-the-grid living, rainwater catchment can provide soft and clear water that’s good for drinking and bathing as well as washing dishes and laundry. But if not properly designed and maintained, the supply system can turn nasty, touching off serious health risk and illness.

A recent spike in cases of rat lungworm disease, a potentially devastating illness in which worm larvae infect a person’s brain, is prompting concerns about whether catchment water could be serving as a conduit. Other ongoing worries tied to the do-it-yourself supply range from exposure to chemical contaminants, such as lead and other heavy metals, to disease-carrying mosquitoes. During a seven-month stretch in 2015-16, Hawaii island saw 264 cases of dengue fever.

While the state Department of Health, which administers laws on safe drinking water, offers education and guidance, catchment is unregulated. The state must step up its efforts aimed at prodding households to be vigilant in self-monitoring this flow used as potable water.

A longtime staple in remote areas, an estimated 30,000 to 60,000 people in the islands depend on catchment systems. About 75 percent of homes in Hawaii island’s Puna district collect rainwater from roof gutters because county water isn’t available.

While spared monthly water bills, those households are tasked with catchment care, which is not labor-free. Tanks must be well sealed to prevent animals and other contaminants from slipping in. Trees and shrubs, which can clog apparatus and serve as nutrition for floating microorganisms, must be cleared away from roofs and gutters. In addition to threats such as leptospirosis, residents in older plantation homes may have to contend with lead paint.

It’s concerning that among residences with rain-catching gear, meticulous upkeep is not presumed indispensable. Hawaii island companies that install and service the systems say that a lot of people are tapping poorly maintained catchments for drinking water. In the wake of 15 confirmed cases of rat lungworm disease in the state so far this year, they’re warning that slugs that can carry the illness are turning up in some catchments.

The University of Hawaii’s School of Pharmacy is now involved in research to pinpoint filters and treatment most effective against the disease. Meanwhile, just-updated guidelines for catchment systems advise careful attention to keeping mollusks and rats (a part of the parasite’s life cycle) out of systems. The Health Department needs to apply more hands-on pushing of this public health message.

Also, amid an increasing demand for off-the-grid getaways, the state should insist that lodgings serviced by catchment provide notice to visitors about health concerns.

Despite risks, there’s plenty of support for catchment (especially non-potable water systems) in this island state, which has limited access to natural fresh water supplies. Population and development pressures and anticipated impacts tied to climate change (sea level rise turning the water table salty, for example) are sending up red flags.

There’s plenty of room to improve water use efficiency. Consider: The Honolulu Board of Water Supply estimates that 50 percent of all potable water it delivers to residences is used outdoors. Further, BWS notes that up to 600 gallons can be collected from just one inch of rain on a 1,000 square-foot rooftop.

In response to calls to initiate state regulation and county extension of municipal water systems to all residents, government officials understandably point to the price tag. It’s simply too expensive for cash-strapped agencies to build infrastructure into lightly populated areas or dispatch teams of catchment cops.

However, state lawmakers should consider tactics such as rebate opportunities for households investing in well-designed systems, and dedicating more funding to help raise awareness and keep in check public health threats.