People cleaning to avoid the new coronavirus shouldn’t flush disinfectant wipes or paper towels down toilets because they could clog drains, back up sewers, and cause overflows at sewage treatment plants, California’s leading water regulator said Tuesday.

Wipes have long been an issue because wastewater treatment plants depend on gravity and water flows, and aren’t often designed to deal with paper towels or wipes, even those labeled flushable. Those items also don’t break down like toilet paper.

The problem has taken on new urgency with the spread of coronavirus, which causes the illness Covid-19.

“Preventing sewer spills is important, especially during this Covid-19 emergency, for the protection of public health and the environment,” the State Water Resources Control Board said in a public advisory.