At international water conferences, Israeli participants always make a point of claiming Israel is the world leader in wastewater treatment and reuse, and indeed this is true. Israel treats over 90% of its sewage and reclaims 80% of it for reuse in agriculture. Only Singapore and Spain come close to this achievement. I too make this claim when I attend such conferences, but I also point out that all of Israel’s water sources are transboundary. All of Israel’s rivers that drain into the Mediterranean Sea originate upstream in the West Bank and most of these rivers are heavily polluted.The reason for the pollution is that unlike Israel, wastewater treatment and reuse in the West Bank is only a fraction of that in Israel. Lacking wastewater and sewage infrastructure Palestinian and Israeli settlement communities drain their sewage untreated into open cesspits or directly into the environment. The result is that the sewage flows into the regions’ rivers and streams, blighting the landscape, posing public health risks and most importantly contaminating the precious groundwater resources that Israelis and Palestinians both use for drinking. Indeed, the most serious environmental hazard in the West Bank is untreated wastewater, but sewage does not recognize borders and this untreated sewage is as much a problem for Israel as it is for the communities in the West Bank.According to a recent report from Israel’s Civil Administration, the body responsible for environmental management in the West Bank, 82.5% of Palestinian sewage is disposed of into the environment, an amount of around 60 mcm/year. In Israeli settlements the amount of untreated sewage discharged into the environment is around 12% or around 2.5 mcm/year.The reasons for this large disparity in wastewater management between Israel and the West Bank is a complex mix of politics, financing and capacity. Many plans for the implementation of centralized wastewater treatment facilities to service Palestinian towns and cities get mired in disagreements on whether or not to connect Israeli settlements to such infrastructure and an arduous process of permitting and approvals, according to the Joint Water Committee that was set up under the Oslo II accords to manage such projects. However, many Palestinian communities are off grid, meaning they do not have access to a sewer network and without a network they cannot connect to centralized wastewater treatment facilities. The result is that sewage is disposed of into cesspits or directly into the environment.The Arava Institute’s Center for Transboundary Water Management, together with Palestinian partners, is promoting a decentralized response to wastewater management in these off-grid communities where sewage (black water) is disposed of in sealed septic tanks and greywater from the kitchen and bathrooms is treated and then reused for localized agriculture. This onsite approach to wastewater management both reduces the flow of untreated sewage into the environment, helping to reduce the flow into the transboundary streams and rivers, and provides an additional source of water for irrigation for these agrarian communities.The decentralized approach is just one way by which, working together, Israelis and Palestinians can help to reduce untreated wastewater discharges into our shared environment. However this kind of approach is not enough. Ultimately, agreements need to be forged between Israel and the Palestinian Authority on transboundary wastewater treatment that will replace the unilateral response undertaken so far by Israel, where it treats the sewage downstream as soon as it crosses the Green Line but charges the Palestinians for doing so. This creates tension between the parties as Israel claims the Palestinians are not doing enough to treat their sewage and the Palestinians charge Israel that they are paying for sewage treatment downstream but do not get any benefits of the treated sewage for use in agriculture upstream.The Arava Institute has recently embarked on a Track II negotiation process to tackle the need for a comprehensive bilateral agreement on wastewater management between the parties. The Track II process is a civil society response that includes experts and organizations from Israel and the PA to jointly promote an agreement that will serve the needs and interest of both sides so that an equitable process of both treatment and reuse can take place. The Track II process also seeks to assist the governments of both sides to formalize such an agreement even in the face of a moribund political process. Water and wastewater management cannot and need not wait for a political settlement, and if we want to once again enjoy clean rivers and streams then we, the public, must demand from our governments to act now. March 22 of this year is World Water Day and the theme for this year is wastewater management. What better way to celebrate World Water Day than with a wastewater management agreement between Israel and the PA.The author is director of the Center for Transboundary Water Management at the Arava Institute for Environmental Studies.